Firmware is up to date.
This is what I've been doing:
I have a personal gmail account (I'll call it personal) and a gmail account dedicated to my Obi100 (I'll call it obimail). I started by sending an invitation to chat from personal to obimail. I logged in to obimail and accepted the invitation. This caused obimail to show up in personal's chat list.
From there, I opened a chat to obimail (from personal), and clicked on the voice call icon (and clicked on "call computer"). I have the personal email address in my circle of trust so after a ring or two, the auto attendant picks up.
From there, I hear the prompt. In the chat window, I hit 3 + Enter to select the callback option.
After the pin prompt, I type in my pin + # + Enter.
After the phone number prompt, I type in a 10 digit phone number + # + Enter.
At this point, *most of the time* nothing happens. I see obimail sign off and if I click the End button in the chat window, Google informs me the call failed because of a network problem (this is the message that is returned if the device drops before the call is ended, further proving the obi100 is rebooting).
I have successfully heard the "Thank you" message once. Every other time, the device reboots before that point.
EDIT: It's probably worth mentioning that the auto attendant works flawlessly when I call in from a phone (NOT google chat).