I, too, was disappointed to learn that my OBI110 can only use a @gmail.com account for GV and not a Google Apps account for GV.
I have had my GV / GrandCentral number for years and it is now part of my Google Apps domain. It is the only number most people have for me. I'm not about to get yet another GV / @gmail.com number to give out to people, nor do I want to move my GV number back out of my Google Apps domain after having just moved it into that domain (for unified contacts).
I was curious about what @jimates has been saying, so I did some testing.
First, I do *not* have a @gmail.com account. Before the recent move of my GV number into my Google Apps domain, I had a NON @gmail.com Google Account for GV.
Second, I signed into my Google Apps domain and successfully placed a number of calls using my GV number over the Gmail web interface using my computer's speakers and microphone.
I then installed a fresh copy of PIAF / Incredible PBX with support for GV using (I believe) the same method as the the OBI110. I fed it my Google Apps domain credentials and was soon making and receiving calls with my GV number with no issues using a PAP2T an an analog phone.
I found it interesting that PIAF / Incredible warns to only use a @gmail.com account. I didn't expect my Google Apps domain account to work, but was pleased that it did.
Perhaps I'm wrong, but all of this indicates to me that the OBI110 firmware is hard coded to use only a @gmail.com accounts.
I hope a future firmware upgrade will allow me to use my GV / Google Apps account as it would make this great device even better.