UncleOp:
With regard to "highly variable" call quality, that would most likely be caused by your Great State of Maine Freezing-ass cold and wet internet connection. VoIP call quality is very sensitive to ISP-related connection quality issues, that you may not notice when performing routine web browsing or streaming, which uses buffering.
If you're using a cable TV company for internet service, you might have degraded signal quality caused by old, damaged or corroded coax cabling and hardware, or a bad cable modem, or any other combination of equipment and wiring between your provider and your house. The same goes for DSL over copper wire pairs.
You can run a VoIP simulation test here:
http://myspeed.visualware.com/index.phpTry several different far-end destinations, and use the G.711 CODEC VoIP test. A score less than 4.0 is problematic, and you'd need to complain to your ISP.
With regard to calling from your Nexus 5, you no longer need to use OBiON. If you don't already have Google Hangouts installed (I believe it's the default messaging program on the Nexus 5), then get it from the Google Play Store. Hangouts can make VoIP telephone calls over your phone's WiFi connection, using your GV phone number as caller ID for outbound calls, and receiving inbound calls made to your GV number.
Hangouts works entirely independent of your OBi device or any Google Chat settings. As long as you're signed into Hangouts, and you've configured it to ring on inbound calls, you can use it for all your GV calling needs.