We observe more and more problems with V72 (handsets loosing registration, hangup).
The misbehaviour might not occur immediately after update but will develop increasingly with usage of the device.
Reason is a bug in memory / list management.

R&D works with high pressure on a bugfix, which will be delivered with V74 in November.

Troubleshooting until availability of V74

a) Downgrade to V51 (depending on infrastructure a provisioning server might try to upgrade the device to V72 again)

or

b) Factory Reset:

 Factory Reset
All individual settings are reset. Warning, your phone will not function after this process and will need to be setup again.

The system PIN will also be reset to "0000" and all additional handsets de-registered

Steps:
  • Remove the cable connections from the base station, both network and phone.
  • Remove the base station mains adapter from the socket
  • Press and hold the blue registration/paging button.
  • Plug the mains adapter back into the power socket.
  • Keep hold the blue registration/paging key (at least 10 sec.).
  • Release the registration/paging key. The base station has now been reset.


    You then need to start again with your device as if just delivered. You need need to enter all SIP details and register handsets.