The release of T-Mobile's myTouch doesn't just mean we G1 owners get new apps (search the Market for "AppPack" and install the T-Mo result to see them all), we get a great new service to compete with one of GV's great features. Visual Voicemail allows you to access your inbox more directly, and, you guessed it, with a visual interface.
To get the service, G1 owners will need to convert their data plan from G1 data to the Android unlimited package. It is $24.95 without messaging and $34.95 with - just like the G1 plans. The new VM comes with the plan, but ask your rep specifically to activate your Visual Voicemail, which can take up to 48 hours (mine took 30 minutes).
If you download and install the app without calling T-Mobile, the program will offer to activate the feature for you. However, at the time of this writing, self-activation is not functioning for G1 owners. (See the last two pictures below.)
Play messages in any order you like, delete them, turn the speaker phone on or off, return the call, or hit the menu and ad a new contact. It's all there, and it's quite friendly. I think I need to publicly compare this program with Google Voice's visual voicemail before too long. To get you closer to the experience, I've pasted some screen shots with descriptions, followed by some T-Mo video of Visual Voicemail in action: