I had a 3GS on O2 and my upgrade is not til dec but I am fed up with o2s service I have decided to buy myself out and now have a 4s with 3 with unlimited data so no worry with any apps draining data trust me you will notice a hell of a difference if you had the 4 then not so much but from the 3GS yes. You will find the screen to be a lot sharper and clear the speed of the phone is great as well as the graphics. siri is new to the iPhone it's ok can be quite entertaining, the camera quality and hd video recording is amazing overall im sure others will agree its the best one out there and I can't see the 5 topping it what more can apple do to a phone that is already at a high spec cons I can't fault it sorry hope this helps