As part of my summer internship I was given a G1 phone for the summer. Also, I recently was invited to the google voice beta. Naturally I wanted to use google voice on my G1 and thankfully google recently released a G1 app for voice. This guide will walk you through the setup process for a normal google voice user and will also walk you through setting up your phone to use google voice for voicemail only.
1) Go to the android marketplace and search for “google voice”
2) After the app installs follow the on screen instructions until you reach this screen:

At this screen, pick the 1st option if you want to use your google voice number as your main number, and pick the other options if you want to keep your current number as your phone number.
3) If you picked the first option in the last step then congratulations, your google voice account is now setup and will act as your voicemail box (go to step 8). If you want to keep your current number as your main number read below.
4) Go to the home screen on your android phone.
5) Hit menu the settings, then go to call settings, the go to call forwarding.

Image from engadget.com
6) In call forwarding you are going to need to change the bottom 3 settings, when you click them you will see something like VM: +1##########, you want to change all of the #’s to your google voice number.
7) Go to the google voice website and then go to settings, then enable the “do not disturb” setting.
8) Enjoy google voice.
PS: If you do not yet have google voice go to http://www.google.com/voice to request and invite.
August 5th, 2009 on 5:39 am
Cool, thanks for this post. I just set up GV on my G1!
Greg
September 8th, 2009 on 10:10 am
How long does it take to receive an invite???
September 15th, 2009 on 5:05 pm
It took me about 1 week to get one. But I bet that it varies based on when google decides to add more testers.
October 9th, 2009 on 5:49 pm
DOESN’T WORK WHEN U TRY TO CHANGE IT ON THE PHONE IT SAYS UNEXPECTED RESPONSE FROM NETWORK…
October 11th, 2009 on 10:52 pm
@brandon, this is likely due to a poor connection. Try moving to an area where you get better cell service and try this again.
October 28th, 2009 on 2:31 pm
“unexpected response from network” here too. ive got 3g and -1 bar from full signal!
??
October 28th, 2009 on 4:36 pm
Bars are not always a good indication of the quality of the connection between your phone and the cell tower. Try moving to another spot and trying it again. Also you might have to hit the “call forwarding” button a few times before it will actually work and show you the options dialogue.
January 24th, 2010 on 8:18 pm
In a family plan, is there a fee or charge to the carrier for using GoogleVoice when calling other local area code numbers?
January 24th, 2010 on 8:42 pm
The carrier fee for using google voice is whatever fee you would be charged for calling your specific google voice number. For example if you live in area code 310 and your google voice number is 310-555-9599 and you use google voice to call area code 530 then your carrier would treat this call as a local call, but if your google voice number is 202-555-9599 and you use it to call a 310 number then even though you live in 310 your carrier would treat this call as a long distance call because your google voice number is long distance.
June 14th, 2010 on 9:37 am
It force closes on me. I am using the g1 on at&t
June 14th, 2010 on 9:38 am
It makes me force close, i am running the at&t network on my g1
June 21st, 2010 on 5:27 pm
I was also running my phone on AT&T when I did this. You might want to try going to an area with better coverage and trying again.