Does the OBi indicate it is successfully registered with the provider?:
Status -> System Status -> SPx Service Status -> Status
SIP registration is required to receive incoming calls, but is frequently not required to make outgoing calls. If the OBi is not registered, double-check the SIP credentials:
Service Providers -> ITSPx -> SIP -> ProxyServer
Voice Services -> SPx Service -> AuthUserName
Voice Services -> SPx Service -> AuthPassword