Buying yourself a T-Mobile G1 off eBay? Better hope that it's either unlocked or that you can get yourself an active T-Mobile SIM card. The G1's much-vaunted first step during the setup is to enter your Google login username and password. Once that happens, the G1 attempts to connect to Google's servers to get your email, contacts, and calendar set up.
Here's the thing, though, if (or when) the G1 cannot connect to the servers, you're done. There is no way to exit out of the Google setup screen, no clear way to reset the phone to bypass it (even in "safe mode"), no way to turn on WiFi. You basically have a sweet phone that can only made emergency calls.
In other words, you're stuck. We're on the phone now with T-Mobile to see how their representative manage trying to activate the device remotely. Stay tuned!