I have just setup my Obi202 for use with GV and two RingCentral lines. The GV service works for both incoming and outgoing but RingCentral only works for outgoing. I have the RingCentral lines set to ring out to their respective phone ports and it appears to be correctly provisioned as it states they are registered successfully. Incoming calls to the RingCentral lines are going straight to voicemail.
The Obi202 is behind NAT with a static IP and UDP ports 5060-5090,10000-20000 are forwarded to it.
edit: I have now tried having the Obi202 device as DMZ and still doesn't receive calls, so I don't believe it is a NAT issue.