Just a quick tip that I haven’t seen referenced too much for those of you who are deploying Call Via Work for Skype for Business. If you’re attempting to make a call and you received the following error: “Call controls are unavailable due to network issues. You can still use the call controls on your desk phone.”, you should be aware that the client is making a UCWA request to the front end server through the external web services FQDN.
This FQDN will need to be published internally and should redirect requests received on port 443 to port 4443 on your front end server. This is typically done through the use of a reverse proxy. To determine your external web services FQDN, it’s as simple as checking your topology builder.