I'm using StraightTalk with an ATT SIM. The "standard" GSM codes for setting call forwarding don't seem to work, nor do the ones suggested in the Google Voice settings menu. I've found a few that do work, may not be news here - and may help someone out. *#61# gets current forwarding status (number and delay) **61*+1xxxyyyzzzz*11*30# sets forwarding to xxxyyyzzzz after 30 seconds of no-answer ##004# resets forwarding to default If you're having a problem with a mobile phone in a ring group handing off to voicemail (which, if not setup will still give a "voicemail not setup" announcement) too quickly, you can *#61# get current status **61*+1[number you just got]*11*30# set to max timeout (30 sec) I've experimented with setting the forwarding number to a vitelity DID. Call comes through with CID of caller (not forwarding phone or network), so I probably need to get a DID per user in order to forward mobile-direct calls to user-specific PIAF voicemail.