Now that everybody's rolling out 4G mobile data, it's time to compare data plans - and in particular, how much data you can use each month.
While Three promises all-you-can-eat data when itlaunches in December, the other operators will cap your downloads according to your data plan, even on the most expensive tariffs.
So which one's best, and how much data do you really need? Let's find out.

Who offers what?

To keep things simple we'll compare each provider's SIM-only 4G plans; if you need a 4G handset too you should of course expect to pay a little bit more.
EE's cheapest plan is £21 per month for 500MB, rising to £36 for 5GB and £61 for 20GB if you sign up before the end of October.
Vodafone's cheapest is £26, but you get 2GB. The most expensive plan is £36 per month and gives you 8GB.
O2's cheapest tariff is also £26, but the data allowance is 1GB. £31 gets you 5GB and £36 gets you 8GB if you sign up before the 31st of October.
Three says its tariffs will be the same as 3G, so that should be around £12.90 for unlimited data.

How much data do you need?

This is a bit of a "how long is a piece of string?" question, because the amount of data you use will of course depend on what you do. If all you use your handset (or tethered tablet or computer) for is checking email and browsing the web, you won't go through much data - but once you start streaming and downloading the numbers soon add up.
It's important to think about what data you might use rather than just look at the amount of data you use now: for example, you might barely bother with YouTube clips or HQ streaming on your current 3G phone because your connections isn't good enough.
Given a faster, more reliable connection, which is what 4G is all about, then your usage may change dramatically.
Here are some numbers to think about:
Music streaming (average quality, 160Kbps): 1.2MB per minute, 72MB per hour
Music streaming/downloading (320Kbps): 2.4MB per minute, 144MB per hour
iPlayer video: 50MB to 225MB per hour
Netflix video, SD: up to 0.7GB per hour
Netflix video, HD: 1GB to 2.8GB per hour
Photo uploading: 5MB per photo
Online gaming: 5MB per hour
[sources: Spotify, BBC, Netflix, Verizon Wireless]

What does that mean in practical terms?

Let's take a real-world example: you stream an episode of your favourite sitcom on the train (50MB), check Twitter whenever you're waiting for the lift (2MB), upload a photo of your lunch (5MB) and stream a few songs as you jog around the park for twenty minutes (24MB at average quality).
That's 81MB in one day. Keep it up every weekday and you'll go through 1,620MB (1.6GB) in a four-week month - and that doesn't include any incoming emails or smartphone app updates.
Maybe you're not so keen on streaming but you're a social media addict. You average five photo uploads per day (5MB each) and spend around fifteen minutes a day clicking on people's Facebook updates and photos (5MB in total). That's 30MB per day, which works out at 840MB if you do it every day in a four week month.
Perhaps you just want to use your 4G phone to tether your laptop, browsing around 30 web pages per day. The average web page is now 1MB, so that's 30MB per day or 900MB per month.
According to Vodafone's figures, which use slightly different numbers to ours, if you don't stream anything but make 12 social media posts, send or receive 12 emails and use 12 websites or apps every day, you'll use 510MB per month. Add 12 minutes of streaming music and 12 of streaming video and you're looking at 2.09GB.
Fancy busting through the 8GB barrier? To do that, Vodafone reckons you'd need to stream 36 minutes of video, 120 minutes of music, make 48 social media posts, send and receive 56 emails and look at websites or apps 30 times per day.
You can minimise those numbers, of course: you might download your music for offline listening, or use Wi-Fi wherever you can (EE, O2 and Vodafone all offer Wi-Fi minutes as well as mobile data). But the numbers give you a good indication of just how much data you might need for everyday activities. As you can see, you don't need to be downloading enormous amounts of data to exceed the cheaper plans' limits.

Are the networks having a laugh?

Left to their own devices, companies will try to offer as little as possible for as much as possible - but once things get competitive, they're usually forced to raise their game or fall by the wayside.
There's already evidence of that happening: with rivals' 4G launches imminent, EE decided last month to double the data allowances on its £26 per month tariff and up its £51 per month plan from 5GB to 20GB for anybody signing up before the end of October.
As the various networks roll out beyond the initial handful of locations we'd expect competition to become more fierce - and we can't wait to see what happens if Three keeps its promises and offers 4G connections for 3G money come December.
One thing's for sure: the prices and plans available today will look fairly stingy years or maybe even months down the line.
Is it time to sign up? Let's ask consumer magazine Which? its advice: Consumers should "not upgrade" because coverage "is too limited" to make the cost worthwhile. Phone users should wait until "coverage improves outside big cities."