Source: http://feeds.gawker.com/~r/gizmodo/full/~3/430782975/use-the-t+mobile-g1-without-activating-it
If you don't wanna spring for the two-year contract or wait out the 90 days 'til T-Mobile will unlock the G1 for you, getting it going without actually activating it is remarkably easy. Just snag an active T-Mobile SIM card from a friend (or foe), pop it in to get through the setup process, and after enabling Wi-Fi, you can drop it like it's hot. 'Course, it won't make any phone calls, but that's not why you wanted a G1 anyway, right? [Love for Biz via Ubergizmo]