For me, the killer feature of Android 2.2 (and the Nexus One) is the built-in wifi tethering support. T-mobile is kind enough to not charge for this feature. Fi

For me, the killer feature of Android 2.2 (and the Nexus One) is the built-in wifi tethering support. T-mobile is kind enough to not charge for this feature. Find out if you can run Android 2.2 on your phone, and if (or how much) your carrier will charge for it. For N1+Tmobile, the answers are "Yes", and "No extra charge".