It's very sad that the standard time sync via NTP has been completely turned off with these phones! I don't understand why these phones have a problem with time derived by NTP and why this was causing problems with messages from CUCM. If a phone is able to retrieve the time by NTP, it should only use this time reference for the time shown on the display of the phone and ignore any time stamps in SIP messages.
I really like these phones and have used them in some (small) installations, e.g. at home without CUCM. Of course the phones are still working properly with CUCM, no question, but it's very sad that Cisco has turned off this important feature without ANY way to turn it back on. It can't be very complicated e.g. to rename the parameter in the xml file or simply to tell admins to remove the ntp reference in CUCM to turn on time sync via SIP register message in case they have any problems.
To me it looks more like a "quick and dirty" solution to fix an issue that I do no understand in detail and to move away from a standard method. As far as I can see the method via SIP register method does not follow any standard and is a proprietary extension to the SIP protocol.
With the argument from TAC that that these endpoints are only supported in UCM you have no other choice than to accept it, but again it's very sad that Cisco has not implemented any way to turn NTP on again.
