iPhone 4S: Users report problems with new SIM cards. I would like to point out that I find it particularly unpleasant when such problems occur with me. Bugs can please have The Others (tm), ok? Definitely not only occurs with previously used MicroSims and turning off the SIM PIN only brings half the relief: then the miserable slow SIM unlocking is better, but the network connection still drops. The last time at least it helped to simply turn mobile data off and on again, but this is not a solution, as you don't notice it directly and therefore in the time when the phone desperately tries to get a connection outside, the battery is sucked dry. Bah.