Sadly, one way or another the phones will all need to be rebooted but you could use this method to at least do them one at a time. After changing the time-zone setting you could follow these steps. This way not everyone would be logged out at the same time;
This command works with the vendorConfig section of the Sep*.conf.xml configuration file, which is read by the phone firmware when the Cisco IP Phone is booted up. Certain phones, such as the Cisco Unified IP Phone 7906 , 7911, 7931, 7941, 7942, 7945, 7961, 7962, 7965, 7970 , 7971, and 7975, obtain Coordinated Universal Time (UTC) from the clock of the Cisco router. To display the correct local time, the time display on these phones must be offset by using this command.
This command is not required for Cisco Unified IP Phone 7902G, 7905G, 7912G, 7920, 7921, 7935, 7936, 7940, 7960, or 7985G.
For changes to the time-zone settings take effect, the Sep*.conf.xml file must be updated by using the create cnf-files command and the Cisco IP phones must rebooted by using the reset command.
First off you are most welcome! Good work on this. Here is a good clip of what the cnf files do;
Configuration Files for Phones in Cisco Unified CME
When a phone requests service from Cisco Unified CME, the registrar confirms the username, i.e. the phone number for the phone. The phone accesses its configuration profile on the TFTP server, typically the Cisco Unified CME router, and processes the information contained in the file, registers itself, and puts the phone number on the phone console display.
Minimally, a configuration profile contains the MAC address, the type, and the number phone number that is permitted by the registrar to handle the Register message for a particular Cisco Unified IP phone.
*** Here is what you changed *** Any time you create or modify parameters for either an individual phone or a directory number, generate a new phone configuration to properly propagate the parameters.
By default, there is one shared XML configuration file located in system:/its/ for all Cisco Unified IP phones that are running SCCP. For SIP phones directly connected to Cisco Unified CME, an individual configuration profile is created for each phone and stored in system:/cme/sipphone/.
When an IP phone comes online or is rebooted, it automatically gets information about itself from the appropriate configuration file.
The Cisco universal application loader for phone firmware files allows you to add additional phone features across all protocols. To do this, a hunt algorithm searches for multiple configuration files. After a phone is reset or restarted, the phone automatically selects protocol depending on which matching configuration file is found first. To ensure that Cisco Unified IP phones download the appropriate configuration for the desired protocol, SCCP or SIP, you must properly configure the IP phones before connecting or rebooting the phones.
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