Android's built-in Amazon MP3 service, offering six million tracks dipped in acid and cleansed of DRM, is certainly a juicy plum, but listening to those tracks on the first HTC G1 on your cans isn't going to be easy: there's no standard 3.5mm jack. You'll have to buy an adapter.
This isn't much of a surprise. HTC's Touch series also eschews the standard, opting instead for an ExtUSB connector that ties microphone, power and headphones into one. You won't be totally out-in-the-cold: HTC will bundle the G1 with a built-in headset, probably of the usual crap bundled-in aural ergonomic design: a set to jaggedly tear at your penichrondiums and which must be thumb pressed down to the cochlea to prevent plopping out.
That's disappointing and a bit puzzling: the G1 is going head-to-head with the iPhone, so you'd think they'd have learned from the iPhone's mistake of a recessed 3.5mm jack. Instead, HTC's topped it, forcing most people who want to listen to music on their phone to waggle around a doofy dongle. That may seem like a small nitpick, but for people who want a phone that is as much a music player as anything else, another peripheral to lug around is a big tick in the "con" column.