[tphone]

Yes, it's possible using TTS from the market. I don't like the voice much, it seems they tried and succeeded in making it sound like the android robot.
Many apps are TTS aware, you just have to search for them among the thousand of them out there. There is also an app to announce your calendar appointments.
One other thing I forgot to mention. It's very nice to make changes on your Google calendar and have the changes on your phone almost before you pick it up.