G1 cupcake upgrade
I’m using a T-mobile Android G1 on AT&T network. I don’t have a T-mobile SIM at all, and I wasn’t getting the Cupcake upgrade through the system menu, either when using AT&T EDGE or using WiFi.
So I followed this guide: http://www.androidandme.com/2009/05/guides/beginners-guide-for-rooting-your-android-g1-to-install-cupcake/
Worked great and easy/no-hassle to follow for an Android n00b like myself. Best and most comprehensive one I could find.