You're a Spotify streaming, Sky Go-ing, YouTubeing modern man or woman, so of course you want a 4G phone.
But could you end up paying a fortune for data allowances you don't use, or hitting a download cap because you haven't ordered enough?
If you're baffled by bandwidth or don't know how much you'll download, we can help.
Who offers what?
To keep things simple we'll compare SIM-only 4G plans, because phone subsidies make it really difficult to compare different providers' pay-monthly plans. Of course data is data whether your contract is SIM-only, pay as you go or pay monthly.
EE's cheapest 4G plan is £9.99 per month for 250MB of data, rising to £12.99 for 500MB, £15.99 for 2GB and £21.99 for 5GB. The most expensive plan is £27.99 per month for 10GB.
Those plans all include texts and calling too. If you just want a data SIM for a tablet you'll pay £10 per month for 1GB or £15 for 3GB.
Vodafone starts at £14 per month for 500MB, rising to £17.99 for 1GB, £22 for 3GB, £27 for 6GB and £32 for 10GB, and again those plans include calls and texts. Data-only plans start at £10 for 1GB and then it's £15 for 3GB, £21 for 5GB and £26.00 for 8GB.
O2 charges £13 per month for 500MB, £16 for 1GB, £20 for 2GB, £24 for 5GB and £30 for 8GB. For data only it's £8 for 500MB, £10 for 1GB, £15 for 3GB, £20 for 5GB and £25 for 8GB.
Three starts at £7 per month for 500MB. £10 gets you 2GB and £15 gives you either 4GB or "all you can eat data" depending on the plan you choose.
All you can eat is effectively unlimited at home and also gives you up to 25GB of data use when you roam in a "feel at home" location abroad, although that roaming doesn't cover you for personal hotspot use. For tablets, Three charges £5 per month for 250MB, £7.50 for 1GB and £15 for 10GB.
Great. But can you actually get 4G?
You might have noticed that O2 calls its 4G plans "4G ready" and Three promises 4G at no extra cost where it's available.
That's because 4G isn't everywhere yet, and of course there's no point in paying for a package if you can't use it. If you're considering a 4G plan don't just check coverage for your home: check where you work and play, and where you tend to travel to or commute.
Make sure you compare like with like, too: coverage maps typically differentiate between indoor and outdoor coverage, and some areas get the latter but not the former.
Okay. How much data do I actually need?
That very much depends on what you do. If all you use your phone, tablet or tethered computer for is checking email, browsing the web and fighting people on social media you'll barely use data at all. If you're streaming HD movies, you'll use loads.
It's important to think about what you will do rather than what you currently do. You might not do much streaming at the moment over 3G, but you may well do with a whizzy 4G connection.
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 15 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.
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Writer, broadcaster, musician and kitchen gadget obsessive Carrie Marshall (Twitter) has been writing about tech since 1998, contributing sage advice and odd opinions to all kinds of magazines and websites as well as writing more than a dozen books. Her memoir, Carrie Kills A Man, is on sale now. She is the singer in Glaswegian rock band HAVR.