Hello. I'm trying to sell my iPhone 3GS 4.0.1 that I unlocked but I need to know for sure if it's unlocked and will work with T-Mobile. I installed ultrasn0w but I don't know anyone with a T-Mobile SIM that I can try it out with. I have heard that you can test it buy simply using another AT&T SIM card, which I did, and I was able to make calls with it. Can you normally use other AT&T SIMs without unlocking it? Thanks, much appreciated guys.