That is incorrect. If you have updated with a Pwnage Tool Custom IPSW, then installed ultrasn0w you indeed have a working phone.
What is throwing you is the carrier logo is missing.
If you did not update with a custom Pwnage Tool IPSW, then you must wait for dev team to finish unlocking 3.1. As of yet the newest baseband is still locked.
But my question is related. Where is the carrier logo? With T-Mobile its just not there any more. If I put an AT&T sim in it show up just fine.
Maybe they just removed it and it needs to be replaced. Any one know how to do this?