Thanks for posting! In current firmware, if the received expire time is equal to or less than our default registration threshold (300 seconds), the result is the 5 second registration renewal you observed on your unit. You will need to modify the registration threshold to a number that is less that the expire time given from the registrar. For example, I would add the following to your SIP trunk configuration.
voice trunk T01 type SIP
registrar threshold absolute 30
This command tells the unit to renew the registration 30 seconds prior to the expiration. The result should be that your registrations will only happen every 270 seconds.
Thanks David! That worked!