asterisk users - Jun 2007 - Aastra 57i / 57i CT phones fail to re-register

Hi,

Has anyone had experience with the Aastra 57i / 57i CT phones?

The problem I'm having is that the phone isn't re-registering itself
with the Asterisk server.  As a result, the phone loses the
registration with the server and is no longer able to receive incoming
calls.  Outgoing calls work fine.

Right now, I have the following sip registration settings:
sip registration period: 180
sip session timer: 30

.. But I've tried other settings but it doesn't work for me.  I have
Polycom phones as well and they work perfectly.

Perhaps it's something I'm missing in the configuration?

Thanks,

Julian

Running firmware:
Firmware Version	2.0.2.1040
Firmware Release Code	SIP
Boot Version	2.0.1.1055
Date/Time	May 4 2007 19:58:37