The IP phones will get their time from the callManager server. Just as with any Microsoft PC, the CallManager server can be setup to automatically adjust the time for day light savings time. To do this, click on the clock in the system tray, Click on the time zone tab, click the Automatically adjust clock for day light savings changes.
Field Notice: FN - 62669 - U.S. Daylight Saving Time Policy Changes for Cisco CallManager/Communications Manager:
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_field_notice09186a00807e02b1.shtml
