I currently have att and I have two lines with my 8800. My bill has slowly climbed to the 160 plus range so Im wanting to make the switch to tmobile. My question is about tmobile sim cards. Do they use sim cards? If so can I unlock my cingular branded 8800 and use it on tmobile? My 8800 is only a few months old so I really dont want to purchase a new one from tmobile. Thanks in advance