T-Mobile G1 up and running with no activation

[wraggster]

It looks like getting up and running on an unactivated G1 is going to be a little easier than Apple made it for iPhone users. No jailbreak required. All you really need to do is beg, steal or borrow an active T-Mobile SIM card and slip it in the phone for the duration of the setup process (it should only take a few minutes). Once you've enabled WiFi you can go back to your old SIM: you're ready to browse the web, run your apps and do everything you expect your Android-powered phone to do (except talk on the phone). If you'd like to get in on this action, check out the read link for the step-by-step instructions.

http://www.engadget.com/2008/10/23/t-mobile-g1-up-and-running-with-no-activation/