Get a new phone whenever you want with O2 Refresh
But U.K. carrier O2 has a solution to protect their customers from something like this happening. O2 Refresh is a 24 month contract that removes the cost of the phone from the contract for voice, text and data. Therefore, whenever a new phone comes out that you must have, all you have to do is pay off the balance of what you owe on your current phone and you're free to buy the new phone and begin all over again. And O2 will even pay you as much as £260 ($400 USD) for your old handset to use towards another phone. If you aren't constantly buying a new phone, once your current phone plan is paid off, your monthly plan will consist of only air time which will result in a smaller monthly payout.
The O2 Refresh plans range from a £12 ($18.45 USD) monthly plan for 600 minutes of talk, unlimited text, and 750 MB of data, to a £22 ($34 USD) monthly plan that offers unlimited talk, unlimited text, and 2 GB of Data.That doesn't include the cost of your handset, of course.
source: O2 via Slashgear