ZEDRAY

So you have a T-Mobile G1 running the Android 1.1 firmware, but you don’t have a T-Mobile SIM.  This means you can’t get past the Google Account sign in screen because you don’t have internet access.

Unfortunately you can’t yet access the phone settings to activate WiFi, so the only way to progress is to manually enter an “Access Point Name” configuration for your third party SIM.

Menu > APN Settings
Menu > New APN

Enter the APN settings for your current network.  This is easy if you happen to have another phone lying about, so you can boot it using your third party SIM and scribble down the settings of a relevant APN.