You probably just ripped off the plastic off of your brand new T-Mobile G1 and we've already caught word that there will be an Over-The-Air (OTA) software update for the T-Mobile G1. Wow, that was fast.
TmoNews has the details on the update and basically it'll include enhancements and make all songs from Amazon available for listening. Should you get it? Probably, it's always good practice to eventually move to the updated OS because of basic bug fixes and stability. The update is termed to be small so don't expect much. T-Mobile will likely send a text message to notify those units in need of updating.
To check if you have the new software: Hit Menu>Settings>About Phone>Build Number. The build number of the updated software is RC28. The old one is RC19.