All phone template variables should be customizable from a global and a phone level. We had several values in our Grandstream default template that were not available from the phone provisioning page and we were stuck with either changing the default template or creating a custom template for the phone. Neither option as we have found from our version 14 to 15.5 upgrade are good ideas. If we create a custom template it might not work with the next version of 3cx, if we edit the default it gets overwritten with the next upgrade. Why not add a dropdown list under the provisioning template editor that allows you to change multiple values like the BLF tab of the phones? The first drop down contains the value names like with Grandstream P99, P100, etc and a field to enter the custom value beside it. Users could change as many fields as needed in the default template without modifying the default templates or creating custom ones.