Forward iPhone voicemail to Google Voice » Clicks and Bits
Use:
*61*1234567890# Call Forwarding No Reply (AS NOTED ABOVE)
*62*1234567890# Call Forwarding Not Reachable
*67*1234567890# Busy Call ForwardingThen to cancel
##61#
##62#
##67#
No promises folks, but I am PRETTY sure this is how to setup your cell number so it forwards to Google Voice. Voice mail forwarding is working for me, but I can't remember exactly what I did.
These numbers were provided by the commenter "Ryan" on the clicksandbits.com site.
Also note that the "Do Not Disturb mode" is an option within GV that you may choose to use. It makes ALL GV calls go directly to voice mail. I am not using this feature.