Device overrides:
https://support.viirtue.com/hc/en-us/articles/360030013831-Phone-Overrides
Button Builder guide:
https://support.viirtue.com/hc/en-us/articles/360043603951-How-to-add-buttons-using-Button-Builder-configure-your-desk-phone-
Provisioning devices:
https://support.viirtue.com/hc/en-us/articles/360029913431-Polycom-Yealink-Provisioning-Guide