It appears OBITalk expects the Google Chat address to use the @Gmail.com domain versus @MyDomain.com.
The background is I've had Google hosting a domain for me with a number of user accounts on the domain for a couple of year now. Each user has a valid Google Email & Voice account. The @MyDomain.com GV accounts all function as expected being able to receive, forward and originate calls. The Google Chat address is username@MyDomain.com and not username@Gmail.com.
Google Voice numbers using a Google Chat address username@MyDomain.com do not work. I moved that same Google Voice phone number to a standard Gmail account with a Google Chat address of username@Gmail.com and it worked.
Based on limited testing it appears there is some type of incompatibility with OBITalk and Google Voice accounts with Google Chat addresses not using the Gmail.com domain.
Please let me know if anyone has any questions.