Mastering Office 365 Administration

Routing calls to external phone services 

Unfortunately, there's no capability to put an external phone number into the calling tree at this time. People keep recommending it on user voice, so maybe it will appear some day. Meanwhile, if you're willing to spring for an extra calling plan, you can create a fake user, sign into the Skype for Business client, and forward their calls to any phone number. This requires having a voice plan, but we didn't need to assign the fake user a real phone number; they can make and forward calls without it.