There is an option to enable/disable call waiting for the phone port. This setting will affect all calls coming into the Obi, not just those on your google voice service.
You cannot disable call waiting for google voice at the google voice level. If you receive a call while using the phone port of the Obi, any other forwarding phones listed on the google voice account will still ring.
From the Expert Settings or in th edivice itself
Physical Interfaces -> Phone Port -> Calling Features -> CallWaitingEnable = uncheck both boxes.
