Don't wait for T-Mobile, it took all of 30 minutes to install the software and then download to my phone and install. It is a clean wipe so as long as you have a back up, you shouldn't be too worried about wiping everything.
I just tried it and let it sit for about 5 minutes connected to a WiFi network and the dialer continued to say No Service? I am not sure if it is because I am using my work's WiFi or what.