If you want to play with a G1 (HTC's new Android phone for T-Mobile) in advance, you can download the emulator and do with it almost everything you can do with the actual handset.
- Download the SDK
- Extract the archive
- Download Jeffrey Sharkey's G1 skin for the emulator
- Install the skin in android-sdk-*/tools/lib/images/skins
- cd android-sdk-*/tools
- ./emulator -skin G1