Currently you can only set a TURN server per domain. We have thousands of domains and it has been a massive project to go through and set a TURN server for each domain (and a pain in the A). Especially with a current bug, when you make any changes to the configuration tab, it removes the TURN server settings. 

We would like to have a system-wide TURN server setting in addition to the individual domain settings. If you can make it a domain default setting, that would be great. This was we can propagate it down to the domains whenever we need to make a change.