Features
T-Mobile and Android appear to be hoping that Android Market, where users will be able to download applications made by third party developers (a bit like the iPhone App Store?), will be a compelling feature of the G1 and other Android phones.
Apart from the touch screen and keyboard, the handset also has a trackball. It looks like the touch screen functionality appears to have some degree of gesture-driven functionality, again not unlike the iPhone.
It has 3G (HSDPA) and Wi-Fi connectivity and claims to "seamlessly" transfer between the two. It also has a three megapixel camera
Software wise, it comes with Google Maps built in (but doesn't appear to be GPS enabled) and an email client that syncs with Gmail as well as "most other POP3 or IMAP mail services." Instant messaging is supported by, of course, Google Talk. The origin of the internet browser is not stated. There's built in support for YouTube.