One of my clients noticed, on Monday morning, that most (but not all) of their 7970s were off by an hour (behind one hour). So apparently, they thought it was already Standard Time. The phones were reset and the time corrected as a result of the reset. I check their CCM servers (pub and sub), which are 4.x, and they were correct with regards to the time (the OS believes that it's still DST). So what happened? Does the phone get time info from the server or does the phone calculate that itself? If the phone does get time from the server, does it only do it during resets or do phones check time periodically? The client is worried that the time is going to get messed up again and their going to get calls to the help desk on Monday morning (Nov. 3rd).
Third Generation (Java based) phones do use a different method than phones like the 7940/7960. I'm guessing that you may be hitting this bug related to phone firmware older than 8.2.2
The time change for Daylight Savings time may not take affect automatically for a third-generation IP phone running SCCP or SIP loads older than 8.2(2).
The third-generation IP phones are 7970, 7971, 7961, 7941, 7911, and 7906. After upgrading to 8.2(1) or 8.0(4)SR3 to get the fix for the 2007 DST changes this issue may appear.
Reset the IP phone from the CCMAdmin for the phone to get the correct time.
Power cycling the phone will not fix the time.
Further Problem Description:
The root cause of the bug is in the conditions required for the phone to update the time zone. Without this fix the only time the phone will update the time zone is if the clock drifts more than 10 seconds off of the NTP server time.
The title is: Time zone rules do not update correctly on 3rd-gen phones
Integrated in: 008.002(001.010) 008.003(000.023)
I think the other reset that works is stopping CM Service and restarting CM Service
Hope this helps!