I finally got selected to get Google Voice (sorry, no invites to pass along) but I had a devil of a time getting the calls to properly forward. Following the onscreen steps was easy, and my phone was registered with google voice. But actually getting the calls to go to Google voice proved to be more difficult. At first I figured it was just a matter of "bouncing" my voicemails using the call forwarding function in settings>phone, but its not that simple. Instead, one needs to send the call forwarding command (prefix *004* on T-mobile).

I've updated to PR 1.2, but i got an error message when I tried to send the command. After some vigourous googling (hehe) I found that I needed to add a little command to the call-ui.ini file in the /home/user/.osso folder.

Navigate to that file, open it in the text editor of your choice and simply add:

[supplementary]
ssc=1

(you did make a backup of the original file just in case, right?)
Just to be on the safe side, I rebooted the n900 and then tried sending the command again (*004*GVnumber#). The first time, I think my reception wasn't very good, but the command went through on the second try. I still cannot just hit "voicemail" to get to Google voice, but i have GV set as its own contact with a shortcut on my desktop.

Meme, are you calling your new Google number, or the Google Voice number (the one that functions as your new voicemail) If you call in to the voice mail, once you enter your pin you can hit 2 for calling out again. i believe the "google number" is essentially like a forwarding number that will ring any associated phones.