I must admit, since I got the iphone 4s my cellular data usage has gone through the roof. o2 shop said my average usage was less than 100mb a month with my iphone 3gs. Within a week of owning the iphone 4s I went through 70mb, and didnt do everything different to normal. I've had to turn off cellular data until I get my usage changed at the next billing date to save me getting a ridiculous bill off them.
I miss the jailbreak to change the overall look and sounds on the phone, wish I hadnt upgraded to be honest