With the exception of EE, existing mobile networks use 3G/UMTS technology, which is now 10 years old and struggling to cope with the needs of today's data hungry users.
4G/LTE (Fourth Generation / Long Term Evolution) is the next stage in mobile network development and will provide users with much faster data speeds than 3G is able to.
EE has been testing the waters with 4G since October of last year, but to date they've had the market to themselves in the UK. As while EE were able to leverage some of their existing spectrum in the 1800 MHz band, the other networks had to wait till a spectrum auction held by Ofcom in February before they could even start preparing for a 4G launch.
However both O2 and Vodafone have launched 4G networks of their own, so EE is about to have some serious competition, while Three is set to launch its own 4G network in December too, and is set to aggressively undercut the competition in terms of price.
So here's what you need to know if you're thinking of getting your hands on one of those fancy-Dan superfast 4G handsets everyone keeps going on about these days.

What differences are there between the 4G frequency bands?

4G can be a confusing beast, particularly when there are three different frequency bands in use in the UK alone.
The 2.6 GHz band is one of the two frequencies that were auctioned off by Ofcom in February. It has a greater data capacity than the other two bands so it can deal with loads of people connecting at once, but it doesn't fare so well over long distances, making it ideal for cities and other compact, densely populated areas but not so good for rural locations.
The 800 MHz band is the other spectrum that was sold off in February. It was used to provide analogue terrestrial TV, but has been freed up since the big Digital switchover.
While it doesn't provide the same data capacity as the 2.6 GHz band, the 800 MHz frequency can easily travel over long distances and will be used to provide broadband speeds to rural areas where telephone exchanges can't reach.
Being low frequency it's also better at penetrating walls than the 2.6 GHz or 1800 MHz bands, so it will provide an improved signal when indoors.
The 1800 MHz band is used by EE and once Three launches a 4G network of its own in December it will be too, thanks to purchasing a chunk of it from EE.
However, as part of the deal to get the spectrum off the brand formed from the merger of T-Mobile and Orange, Three had to agree not to launch 4G on the spectrum before October 2013, which is the main reason for it delaying its deployment until later in the year.
The 1800 MHz band strikes a balance between coverage and capacity (falling between the extremes of the 2.6 GHz and 800 MHz bands) which makes it a good 'middle-ground' for getting 4G around the country.

Ofcom's 4G spectrum auction

The 4G spectrum auction held by Ofcom at the beginning of the year saw winning bids from O2 (Telefónica UK), Vodafone, Three (Hutchison Whampoa) and of course EE. Interestingly BT also came away with a piece of the pie through its subsidiary Niche Spectrum Ventures.
Remember, more MHz means a better connection, so the more 'x GHz' of spectrum, the more widespread and robust a network can be.
Vodafone spent the most at the auction- a whopping £790,761,000 and came away with 2 x 10 MHz of 800 MHz spectrum, 1 x 20 MHz of 2.6 GHz spectrum and a further 1 x 25 MHz of 2.6 GHz spectrum.
EE spent £588,876,000 and secured 2 x 5 MHz of 800 MHz spectrum and 2 x 35 MHz of 2.6 GHz spectrum, which is less spectrum overall than Vodafone has.
Don't forget that EE can also call upon the 1800 MHz spectrum that it's been using over the last year though.
O2 spent £550,000,000 on 2 x 10 MHz of 800 MHz spectrum. The company completely neglected the 2.6 GHz band which may hurt its inner city performance, but with its extensive network of Wi-Fi hotspots in cities the bubbly brand thinks it will be OK without it – although it will be interesting to see how receptive consumers are to the idea.
Three spent £225,000,000 on 2 x 5 MHz of 800 MHz spectrum. Like O2, the company passed on the 2.6 GHz band, however Three will also have access to some 1800 MHz spectrum, as noted above.
BT was something of a surprise bidder and secured 2 x 15 MHz of 2.6 GHz and 1 x 20 MHz of 2.6 GHz spectrum- though it doesn't look like the telecoms giant is going to launch a new mobile network. Instead the spectrum is likely to be used to boost and complement its existing broadband services as well as providing behind-the-scenes wireless support for the mobile industry.

EE's position

4G arrived in the UK on 30th October 2012 courtesy of a joint venture between Orange and T-Mobile named Everything Everywhere, or 'EE' for short.
EE was granted permission by Ofcom to use part of its existing 3G bandwidth for 4G, which is why it got a head start on everybody else in October 2012. As you can imagine, rival networks were somewhat unhappy about this decision, but part of the deal for EE to get this head start was that it had to sell off a chunk of their 1800MHz spectrum.
EE vs O2 vs Vodafone vs Three: which will be the best 4G network?
This chunk was promptly snapped up by Three, though despite getting a hold of 4G spectrum before O2 or Vodafone, Three is going to be the last network to launch a 4G service, which is part of the sale deal with EE.
For almost a year EE was the only provider of 4G services in the UK and it's made the most of that head start as its 4G network is currently available in over 100 UK towns and cities.
If you don't live in one of those 4G-imbued areas you can still buy one of EE's 4G handsets and use the 4G services in any of the above towns and cities, but you'll have to wait a bit longer to get 4G where you live.
Tariffs are still fairly expensive – for example you'll pay £26 per month for just 500MB of data on a 24 month contract with a handset.
However O2's initial prices aren't much better (apart from early deals with a touch more data) and EE has the advantage of far wider coverage.
What's more, EE has access to a huge amount of 4G spectrum and is the only network with access to all three of the 4G spectrum bands that are in use in the UK, making it the best prepared for data demands of the future.
EE has also begun improving its 4G network in certain locations, leading to 'double speed' 4G being available in a number of towns and cities. This means that it's got another technological advantage over O2, Vodafone and Three, but it won't be long until the rest have caught up.

O2's position

O2 finally launched its 4G network on August 29, although there may not be too much to get excited about as O2's launch is limited to London, Leeds and Bradford. However Birmingham, Newcastle, Liverpool, Glasgow, Nottingham, Leicester, Coventry, Sheffield, Manchester and Edinburgh will be added before the end of the year.
Though it can be hard to directly compare each networks 4G pricing, O2 by and large seems comparable to EE's. For example: a 12-month SIM only contract with 1GB of data will set you back £26 a month- which is exactly the same as EE charges.
That said, in a bid to get early customers O2 has got a few temporary deals that are rather more compelling. Before October 31, customers who take out a 3GB data tariff (which starts at £31 if you don't need a handset) will have it upgraded to 5GB for the life of the contract.
Similarly a 5GB tariff (starting at £36 a month on a 12 month contract with no handset) will be upgraded to 8GB of data for the duration of the contract.
Early deals aside O2 doesn't have the coverage to back up its prices so in the short term it seems like a tough sell. On top of that, the fact that O2 doesn't have access to the 2.6 GHz frequency may result in it not having the data capacity to adequately serve 4G to cities once customers become more data hungry.
Another problem O2 faces is that the iPhone 5 isn't compatible with its network, but anyone who purchased an iPhone 5 from O2 between the September 21 2012 and March 31 2013 is eligible for an early upgrade deal, wherein O2 will knock off 25% of the remaining line rental and give you up to £295 for your old handset (depending on model and condition), making it much more affordable to upgrade to a phone that can get 4G.

Vodafone's position

Vodafone is also launching its 4G network on the August 29, seemingly just to steal some of O2's thunder as the network was previously talking about launching later. It also has a site-sharing deal with the effervescent provider, so that's likely to play a big part in making the Aug 29 switch-on more efficient.
Initially Vodafone's 4G signal will only be available in London, but by the end of the year the network will have brought it to Birmingham, Bradford, Coventry, Edinburgh, Glasgow, Leeds, Leicester, Liverpool, Manchester, Newcastle, Nottingham and Sheffield. That's thirteen cities in all, which is the same number as O2 plan to provide 4G to by the end of the year, though still a long way short of EE's coverage.
However Vodafone does have one advantage and that's pricing, as many of Vodafone's 4G tariffs are cheaper than O2 or EE. For example for £26 a month Vodafone will give you 2GB of data on a 12-month SIM only contract.
That's double what either O2 or EE is offering. It could still hardly be called cheap, but it's substantially more affordable than 4G has been to date.
You won't be left high and dry if you're already a Vodafone customer either, as assuming you have a 4G-ready handset then for £5 extra a month you can switch to a 4G tariff- which will also double your data allowance.
Better yet, Vodafone 4G customers who take up a 24 month contract with a handset will also get access to either Spotify Premium (which usually costs £9.99 a month) or Sky Sports Mobile TV (usual price £4.99 a month) for no extra charge.
Whichever service you choose will be free for anything from six months to the full two years of the contract, depending on your tariff.
Much like O2, Vodafone is unable to provide 4G to the iPhone 5, but customers who purchased an iPhone 5 from Vodafone between the September 12 2012 and June 30 2013 will be able to return their handset to a Vodafone store and have 75% of their remaining line charges taken off to minimize the cost of an upgrade.
Similar deals are also available for those with a Samsung Galaxy S3 orSamsung Galaxy Note 2.
With sizable chunks of both the 800 MHz and the 2.6 GHz band, Vodafone should have the capacity to deliver a fast, reliable 4G connection to customers in both urban and rural locations.

Three's position

Three has finally announced it will be rolling out its 4G networks in December of this year, which is a bit later than the Big Three. However, it will have an ace up its sleeve: no additional cost for 4G.
If you already have a 4G handset and a Three SIM then 4G speeds won't cost you any extra - all you'll have to do is install a software update from the network to activate it.
Those on monthly plans with all you can eat data won't see any caps imposed on their data limits either, meaning those running on the One Plan for £15 per month will get unlimited 4G data, and nigh-on unlimited calls and texts (providing they already have a 4G-enabled phone) which will massively undercut Three's rivals.
London, Manchester and Birmingham will be the first cities to get the 4G network, with the switch on set to "accelerate" in January bringing 4G access to over 1.5 million customers in the new year.
By the end of 2014, Three intends to have 4G coverage in 50 cities across the UK, and nearly the whole country covered by the superfast connection by the end of the following year.
This is thanks to the numerical networking managing to nab some of the 800MHz spectrum to deploy 4G speeds to the rural parts of the British Isles, as mentioned above.
That combination of low prices and large data allowances could be enough to topple the scales in Three's favour and may, we hope, force the other networks to lower their prices.
Getting 4G at Three's prices will mean waiting just a little bit longer, but in the meantime there's always the network's Ultrafast service, which is substantially faster than standard 3G.
However, long term things don't quite so rosy for the network, as with only a small amount of 800 MHz and 1800 MHz spectrum it may struggle to keep up with its customers data needs.

4G coverage: When will the whole of the UK have it?

Although all of the networks should have 4G services by the end of 2013, they will of course focus their efforts on major cities first in an effort to service the most users.
Ofcom's targets say that 4G must reach 98% of the population and 95% of the country by the end of 2017, but EE claim that it will cover 98% of the country by the end of 2014 and already cover 60% of the UK population, while O2 and Vodafone are both aiming to cover 98% of the country by the end of 2015, so UK-wide 4G coverage may be closer than you think.
EE are also upgrading their 3G network to DC-HSPA in an effort to improve speeds when 4G services aren't available, while customers of Three can fall back on the networks Ultrafast service.

Are the new 4G phones any good?

The 4G phones currently available in the UK are basically just LTE-equipped versions of current top-end 3G phones, such as the iPhone 5,Samsung Galaxy S4, and HTC One, along with a few mid range handsets such as the HTC One Mini and Nokia Lumia 820.
However, the iPhone 5 won't run on O2 or Vodafone's networks, as you'll see below.
One of the advantages to being late to the 4G party is that we're spared the rubbish "first try" handsets that we suffered back when 3G came out, so don't be shy to try the new 4G phones.
4G handsets are available on every network, though if, as in Three's case, the network hasn't launched its 4G service yet, you'll be limited to 3G speeds for the time being.

Do the 4G versions of the iPad 4, iPad Mini and iPhone 5 work in the UK?

They do! The iPad 4, iPad Mini and iPhone 5 all work on the 1800 MHz frequency band used by EE. However they aren't compatible with the 800 MHz or 2.6 GHz bands that O2 and Vodafone will be using, so you'll only be able to enjoy 4G speeds on the current generation of iDevices if you get one on EE or wait for Three to roll out 4G.
That said it's highly likely that the next generation will work on other frequencies, so fingers crossed for 4G iDevices on all networks before the end of the year.
None of the older iPhones or iPads work with 4G on any UK network, so even when buying through EE or Three you'll have to shell out for the latest and greatest of Apple's offerings.

What are the 4G download speeds?

Well, so far we can only comment on Everything Everywhere's network speeds, as this is the only 4G network with confirmed speeds at the time of writing, but it's certainly impressive.
EE boasts speeds typically five times faster than current 3G networks, though on several occasions we found it to be ten or more times faster than a comparable 3G handset in the same area.
In use it just makes everything feel much snappier and ensures tasks like checking image-laden emails and browsing complex web pages is a breeze.
EE claims average download speeds of 12-15Mbps and typical maximum speeds of 40Mbps, with upload speeds averaging around 5-6Mbps with a typical maximum of 15Mbps.
EE has also started rolling out 'double speed' 4G in select locations. So far it's available in 20 cities and, according to EE, average download speeds in those locations are 24-30Mbps, while the maximum speed is 60Mbps. Average upload speeds are said to be 11Mbps.
EE has achieved this by making network improvements which allow customers to use 2 x 20 MHz of spectrum, where before they would have been using 2 x 10 MHz of spectrum – essentially a bigger (virtual) pipe allowing a faster rush of data to enter your phone.
Whether the other networks will achieve any higher remains to be seen, but 4G download speeds could theoretically exceed 100Mbps with upload rates of more than 50Mbps, though it's unlikely we'll see anything like that in the near future.

Why is 4G so fast?

4G's impressive speed increase is achieved with the use of OFDM (Orthogonal Frequency Divison Multiplexing), a transmission technology used by the likes of ADSL, Wi-Fi, DVB-T, DVB-H and DAB.
Not only does it reduce latency (the amount of time taken to buffer and connect to webpages), but it also minimises interference and is able to cram greater amounts of data into the same slice of radio bandwidth.
Simply put, this enables 4G/LTE phones and tablets to stream video and play online games like never before, largely because 4G has been designed primarily as a data network, rather than a voice one and it uses the same TCP/IP protocols that underpin the internet.
The upshot for you is that the data is 'flatter', as in it's easier for the networks to stream, so should theoretically be cheaper. Whether those cost savings are ever passed on remains to be seen – it's not cheap to roll out 4G, especially at this rate of deployment across the UK.
It's possible that further increases in speed could be achieved with MIMO (Multiple Input Multiple Output) technology, which uses multiple antennas on transmitters and receivers like 802.11n Wi-Fi equipment, but that's some way into the future.
Nokia has reportedly achieved 173Mbps from 4G with a 2x2 MIMO configuration (two antennas on both the transmitter and receiver), so a 4x4 arrangement could potentially offer as much as 326.4Mbps, although this isn't something we need to think about right now… although perhaps we'll see this these speeds on the iPhone 10?

LTE-A and the future of 4G

The UK may only just be fully embracing 4G but some parts of the world are already looking to the next generation of high speed mobile data. That next step is LTE-A (the 'A' is for 'advanced', fact fans).
Essentially its works by increasing the number of antennas in use as detailed above, alongside 'carrier aggregation' which allows a device to combine multiple 4G signals or even multiple different frequencies, rather than just using one at a time as standard 4G does.
In theory LTE-A can deliver far greater data speeds than the 4G of today. In fact it could potentially reach speeds of up to 160 Mbps, which is comparable to a 20MB home broadband connection.
LTE-A won't work on 4G-ready phones as they'll specifically need an LTE-A chip in them, however there is already one LTE-A compatible handset available.
It's an LTE-A version of the Samsung Galaxy S4 and currently it's only available in South Korea- and if you're considering importing it, don't, because of course none of our networks currently support LTE-A.
It's a fairly safe bet that the UK will get in on the act one day and at that moment we'll be able to enjoy fixed line broadband speeds on the move. But the technology is still in its infancy and we've only just got normal LTE, so we've probably got a while to wait.