I love Google Voice as it provides me with a copy of the voice mail and an email with a transcript of the voice mail. I really wanted to be able to use GoogleVoice for all my voice mail needs and today I figured out how to do this and now I dont have to miss important calls while I am in a meeting.
The technology used is called conditional call forwarding. Conditional, because when people call us and the number is either busy, unavailable or unanswered, we want the caller to be forwarded to Google Voice.
I have an AT&T cellphone and here is how I did it:
activate conditional call forwarding by dial the following number (replacing the xxxxxxxxxx with your GoogleVoice number)
To disable call forwarding dial
Information for other carriers: http://www.google.com/support/forum/p/voice/thread?tid=00a93855af6943b4&hl=en