If you want to stream songs or watch lots of video on the go, you'll probably want to have unlimited data - or at least a generous data allowance. But does 'unlimited' really mean you can munch as many megabytes as you like?
In this guide:
Unlimited mobile data plans
"If my price plan gives me 'unlimited' data, is there really no limit to how much I can use the internet on my smartphone?"
Loads of people ask us this question, and with more than half the country now carrying around smartphones, it's more important than ever that people know the answer.
Web-enabled handsets, like Apple's iPhone or the Samsung Galaxy S4, mean we can surf the net, check emails and download apps whenever want. But convenience comes at a cost and the "currency" is data, which in turn costs real money.
So before you sign on the dotted line, it pays to know what you're getting - to avoid expensive bills or cut down on costs by only paying for the data you actually need.
Which networks offer unlimited data plans?
Each of the main 3G networks - Three, T-Mobile, Vodafone, Orange and O2 - has its own approach to limiting mobile data usage. Some contracts clearly state a set download allowance, while others described as "unlimited" may still carry a fair usage policy.
When choosing a mobile provider, it's a good idea to look carefully at the terms and conditions, as some deals will suit your needs better than others.
A summary of each 3G network's policy on mobile data usage is below. And remember - you can compare plans directly with our mobile comparison service.
Three (www.Three.co.uk) prides itself on offering a truly unlimited mobile internet service. It provides "genuinely unlimited" internet use and no danger of bill shock as with more restricted data plans.
T-Mobile (www.T-Mobile.co.uk) offers plans with unlimited data, and no fair usage policy. That means that you can browse, download, stream and listen to your heart's content while on the move. It's worth noting that its parent company, EE, does not offer unlimited mobile broadband with its plans.
EE's 4G mobile broadband plans come with varying data limits, but none of them unlimited. Plans range from 500MB data a month to a massive 20GB data a month. EE will let you know if you're close to hitting your limit, and if you are, you can buy a data add-on to get a little more.
Where mobile internet is included in a Vodafone (www.Vodafone.co.uk) price plan, a set allowance - usually between 250MB and 2GB - will be stated in the contract. Customers can check their usage via the MyAccount page on Vodafone's website.
Data Test Drive is also available to new and upgrading pay monthly customers. It allows people to use as much data as they like - with no restrictions - for the first three months of their Vodafone contract. At the end of the "test drive" the customer can choose a data bundle that suits their actual usage.
O2 (www.O2.co.uk) doesn't offer plans with unlimited data. Its plans range from 100MB a month, to a fairly generous 4GB. O2 lets you know If you're getting close to your limit, and if necessary, you can purchase top ups to get more data.
In the same way that networks charge you to make calls - or restrict the number of free minutes on a 'pay monthly' contract - there are costs involved with connecting to the internet on your phone.
Whenever we send emails, check Facebook or download an app, our device is transferring data, which puts a certain amount of strain on your provider's network.
To help keep traffic flowing, network operators - Vodafone, EE, O2 and Three - pass the cost of running mobile internet to their customers. Instead of paying by the minute, you'll be billed according to how much data you consume.
This makes it important to compare mobile phone deals and choose the package with a data plan that best suits your needs.
Most networks include a set amount of data - usually between 500MB and 2GB - in their pay monthly deals. For an additional charge, extra data can often be provided as an add-on product for both pay monthly and pay-as-you-go customers.
How much data you need entirely depends on what you use your mobile internet for, and how much time you spend using it. The examples below should give you a rough idea of how different amounts suit different types of user:
500MB a month - This is now a typical pay monthly offering of most 3G network providers. It should be sufficient for everyday use of emails, Facebook and Twitter, as well as streaming music reasonably often.
2GB a month - Regularly streaming YouTube videos, movies or TV shows, your data consumption will quickly rocket. You may also want to consider bigger data packages if you download lots of games, media or email attachments.
If you find you need more data, it is usually possible to stay with the same network and upgrade your allowance. Some providers, such as Three and EE, also offer unlimited data plans, though these can often work out to be much more expensive in the long run.
As smartphones become increasingly important in our day-to-day lives, lots of us now opt for unlimited 3G data plans. Confusingly, some "unlimited" deals are actually subject to a fair usage policy, which can end up imposing limits which prove costly when exceeded.
It's an ongoing hot topic - "bill shock" as a growing problem in the UK. It affects people who think an unlimited plan means free internet without limits.
In reality, these people could unwittingly rack up enormous monthly bills - resulting in a nasty shock - because they exceed the network's fair usage policy.
Before signing a pay monthly contract, you should always check the terms and conditions to avoid any hidden costs.
While mobile data plans are often labelled "unlimited" by 3G network providers, usage is normally capped in line with a fair usage policy. This is basically a set of guidelines laid out in the contract's terms and conditions.
Breach the fair usage policy and your phone bill could increase significantly, as additional charges may apply for the extra data you've used. The Advertising Standards Authority (ASA) has looked at the 3G networks' use of the term "unlimited" and given the green light for them to keep using it, so being aware of any limits is crucially important.
To stay out of the danger zone, make sure you understand your provider's fair usage policy. If you think you'd easily exceed it, consider ways of cutting down on your data consumption or look into switching providers.