Try configuring this on the endpoint. For instance, on Sipura ATAs you might set the following parameters if the location were using Eastern Standard Time:

    Time_Zone                         "GMT-05:00" ;
    Primary_NTP_Server           "time-b.nist.gov" ;

We just rolled out service, and a lot of users are complaining about the
time displayed on their phones being incorrect.  Exactly 2 hours behind.

The switch which we receive all of our inbound calls from is 2 hours behind
us.  Is it possible to adjust the time in the Caller ID so that their phones
will display properly?