First, we need the Dev-Team to release their jailbreak tools. Secondly, we need the Dev-Team to release ultrasn0w. Ultrasn0w is the tool that performs the unlock, but can only be installed/used on a jailbroken phone.
Both sets of tools should be available on or before Friday. Dev-Team Blog is the official website -- watch there for updates.
If you update now, your phone will be locked again.
I updated my unlocked Italian iPhone to 3.0 yesterday afternoon. It went seamlessly and took no more than 20 minutes. I've been using my iPhone on T-Mo for about 8 months or so. I have Model: MB500T. I did have to reset my APN settings for T-Mo again to get the Data Network working again.