Anyone successfully using Axon PBX with BT VOIP service ? My Axon PBX
software works very successfully with other VOIP providers, but with
BT there is a (re-)registration issue which I can't solve. I keep
getting error messages every 10 minutes or so:

Registered as sip:44xxxxxxx@btsip.bt.com
then 1 minute later...
Register attempt for sip:44xxxxxxx@btsip.bt.com failed
400 Too many contact addresses

Any advice gratefully received.

David