The time on the IP phone which is registered to Cisco CallManager 4.x shows a different time than it is on the computer. The computer is using a server application to source the time. The IP phone is sourcing the time from the Cisco CallManager.
This issue occurs when both sources are out of sync for the time. To resolve this issue, set up a primary domain controller (PDC) or another server as a Network Time Protocol (NTP) server and then configure the Time Synchronization for Cisco CallManager and all the other servers in the network. In this scenario the Cisco CallManager server is a client server of the NTP server.