(Original post by Luxray)
Wait a few months, the Iphone 5 will be out. Probably in October.
Otherwise when I had a 4S, I bought it from Apple and used Giffgaff (£10, 250 mins, unlimited data and texts, no contract)
Buy it unlocked and cut the sim down to the correct size.
Honestly you really should wait, come-October people will have the iphone 5 and you will wish you waited just that extra bit.
If you really must get it then just go to the apple shop thats the cheapest way you will get it. You can use your sim with the iphone and once the contract finishes then join giffgaff.