I want to get rid of AT&T and switch to TMobile. I know that I will be stuck on 2G/EDGE speeds with Tmobile but the reception from AT&T in Boston is so terrible, I don't care. I have jailbroken my iPhone 3GS iOS 4.2.1. Can I unlock it? If I need to upgrade or downgrade my iOS software, please let me know and I'll follow whatever steps you provide. Thank you!