bullwinkle,
It's even worse than you describe. The OBi's default RegistrationPeriod value is 60 seconds. When left this way, the OBi ignores the incrementing 'expires' value that Callcentric sends, keeping the registration period at 60 seconds. I asked Obihai to increase the default RegistrationPeriod value to at least 600 seconds (most ATA's default to 3600 seconds) a year ago, but my request was immediately dismissed.