Is it possible to have a existing ATT business phone number transferred to ObiTalk or Google Voice?
If you are the owner of the AT&T business line then yes. You'd do the two-hop port -- first port to a cell phone then port to GV as described here: http://www.obihai.com/porttutorial.html
- You want to first heed the warning under "Before you begin, do this first!", see "sanity check," else you could get into the position of porting to a cell phone, but the number (irregardless of what cell phone carrier you choose) may be in as area where GV does not support porting.
Also, keep an eye on this thread: http://www.obitalk.com/forum/index.php?topic=6867.0;topicseen
It seems using an obi device with GV is suspect until more info comes out.