Do you have sip transparent proxy enabled? A copy of the configuration with passwords and sensitive information redacted would be useful.
did you get this one fixed... i have had a similar problem that was the Adtran was not able to act as a true B2B and do digest on both sides?
These messages are standard responses when the ITSP is doing keep alives to keep the trunk active and check for availability of the Adtran. If the trunk is up and working then these messages can be ignored.