This problem is mostly observed in Cisco CallManager 3.3(3)sr3 and later with 7970 running 5-0-1-0 load and later.
The time appears as Greenwich Mean Time (GMT) because the configuration file is given to the phone with a time zone set to CallManager Time.
The 7970 time zone offset under telephony service and the router's own time zone offset setting have to match. The router sends the Coordinated Universal Time (UTC) time to the phone when the phone registers through Skinny Call Control Protocol (SCCP). The phone then calculates the local time based on UTC and the configured time zone.
If it is 2 p.m. local time in California, then the router needs to send UTC time to the phone, which is 2 p.m. plus eight hours (10 p.m.) Then the phone needs the time zone set to Pacific Standard Time (PST), so that it can subtract the eight hour UTC offset back out. This is because the 797x phone has its own unix-like internal operating system, and it wants to know UTC instead of local time. The 7960 phones etc operate off local time.
To resolve this issue, configure a new date/time group with the time zone the server is in. Update the device pool with the new date/time group and place the 7970 in that date/time group.
The fix for this problem is available in these releases: