Your carrier's data on an AT&T SIM
I can't find the old thread concerning writing your carrier's SIM data on an AT&T, so I made a new one.
I just spoke to one of my tech buddies at Kall Telecom. He said that you CAN write your carrier's data onto an AT&T SIM - and it will work in an iPhone.
However you do need to break the encryption on the card (which shouldn't be a biggie) and it is ILLEGAL - so I'm forgetting that one.
Another thing, when you insert your AT&T SIM with your carrier's IMSI and whatever data is on it - it will only work with YOUR carrier (offcourse). But it's not like it locks your phone or anything.