Phones get the ringtones from the files located in the TFTP server they're pointing to for their configuration files and FW by default, you would need to configure a separate TFTP for those phones and modify such files so that only certain options show up.
the Ringlist.xml file contains all ringtones and get pulled down each time you browse trhough the available ringtones on the phone. There are no separate files for each phone type, so you cant limit the ringtones for just your 7921's, unless (as said by java, you can split TFTP servers)
you can obtain the current Ringlist.xml file from the CUCM CLI by issuing
file view Ringlist.xml
modify this file and upload it (to each server in the cluster) using TFTP (got to your OS administration->Software upgrades -->TFTP filemenagemnent
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.