Set the following parameters in the Obi configuration interface (or corresponding parameters in ObiTALK portal).

Service Providers -> ITSP Profile B -> SIP -> ProxyServer : sip.callwithus.com
Service Providers -> ITSP Profile B -> SIP -> RegistrationPeriod : 120

Voice Services -> SP2 Service -> X_ServProvProfile : B

Voice Services -> SP2 Service -> AuthUserName : username
Voice Services -> SP2 Service -> AuthPassword : password