Another work around that seems to be working for me atm, is you must do a hard transfer by dialing the full google voice number of the extension you are trying to transfer to (not the obitalk number nor any extension or number code has worked for me thus far ..only this)
Example- Call comes in and i answer on Phone 1, i then want to transfer to Phone 2, so i hit the transfer button and then dial phone 2's full google voice number (in my case (407) 984-****) and then hit transfer... Phone 2 will then start ringing (they must answer before you hang up Phone 1), but once they've picked up the line your free to hang up Phone 1 and the call will not drop!. I haven't tested this in a scenario where Phone 1 or 2, have people on hold or other calls coming in , but in a silent environment it works reliably.
*TIP - If you dont want to have to physically dial the destination phone's full google voice # everytime then simply save them into your Contacts that way u can simply scroll to there name and hit the 'call' button instead.