At&t I-phone 4 unlock for Tmobile?? help please.?

Im gonna buy this tomorow for 500$. I need to know more information before I buy it. The guy gonna sale me say that the phone modem firmware is 02.10.04 so when the iOS4.3 releases on 3-11 and the GreenPois0n is released this will be fully useable on Tmobile. Is it true?

ot sure about the GreenPois0n unlock. But there are certain unlocks like the one from Wickedunlock.com which does not depend on firmware and which is permanent. They offer this through remote service and hence the iPhone can be unlocked from home.