Can a Sim Card Cause Battery Drainage?

Had my iPhone 3G since it was launched in UK & was on Monthly contract. Now my contract with O2 has ended I decided it would be cheaper for me to go on to O2 Pay & go, Contacted O2 & they send me a Pay & Go Sim card & transferred my Monthly contract Number over to the Pay & Go Sim.

Know battery life on iPhone isn't the best but when I was using my monthly sim I was getting at least a good 24 to 30 hour use from my iPhone before having to recharge, Now since using the Pay & go sim i am only getting about 12 hour usage before a recharge is needed.

Would a change of Sim cause battery life to change, Does 3G use more battery power on Pay & Go? Would be good to know if anyone else has had the same problem or could answer my questions.

Thanks