I have just recently unlocked my off contract AT&T iPhone 4. I would like to test it out using a T-Mobile SIM. Do they use Micro SIM or the old standard size? And if not, I've seen and heard that people can easily modify the SIM down to Micro size. But once it's been trimmed, you won't be able to put it back into the original t-mobile phone again? Not sure if all tmobile phones have been updated to use the micro-sim or what not so I'd like to know before I start trimming. This is just for testing my unlock, and then I'm putting the sim back to brother's phone (tmobile).