I'm currently using a iPhone 2G on a 2.2 firmware. Recently I've been experiencing weird problems after I upgraded my sim card to a 3G one. I would start a sms conversation with someone and after a few exchanges, I can't seem to receive any more text messages, though I can still send out. It seems that the problem only occurs with a particular carrier and I have no problems with other people on my contact list. I wondered if its my sim card or the iPhone. Perhaps anyone who experienced something similar, can give me some pointers?