Hello Suchi, I had a similar situation where the customer did not want to do firmware upgrade with the CUCM upgrade. Before Upgrade switch all phones to DP where they are not registered with the Pub. At CUCM go to Device> Device Setting> Device Default locate your phone type SIP or SCCP Copy the name for default firmware version which this type of phones use by default. Save if in notepad. Do the upgrade for the Pub After upgrade go to the same path  Device> Device Setting> Device Default locate the new file name for the firmware used with your name. copy and save the file to a notepad. change the new file name for your phones model to the one you saved before the upgrade. switch the phone to the DP using the Pub, and the phones will reboot and won't do firmware upgrade. do the upgrade to the remaining CUCM nodes. change the phones' DP to their original ones before upgrade. Now all your phones still with the old firmware. and your cluster got upgraded. if you want to upgrade them, but not all at once to save your WAN bandwidth : change the name at device default to the new one "you saved after the upgrade" Restart the phones. one by one, 10 by 10 or the best way to you. Phones will get the new firmware. Regards. Mohamed Helmy ... View more