Use my mac mini to make phone calls

The Continuity feature that allows your Mac to make calls doesn't really have a name. Its quite simple to do as well.

Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

Handoff is a Continuity feature, but not making for calls. It's for handing "off" documents and websites between devices for completion. Start a document on your iphone on the train coming home and "hand off" to your Mac when you get home.

The overall requirements for all Continuity features are listed here. Your Mini must have OSX Yosemite or later and you must add an external microphone or headset.

System requirements for Continuity on Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

FaceTime is for FaceTime only calls to other FaceTime users. A FaceTime user can be using a Mac, iPhone or iPad. You cannot do a FaceTime call to a normal landline or receive a call from a landline.

There are programs that do VoIP - Voice over IP on a Mac and you can use a VoIP service to route these to and from landline calls e.g. Vonage, or you can setup your own VoIP to landline gateway.

However I think what you are looking for is a feature Apple added in Sierra to link a Mac to an iPhone so that the Mac can use the iPhone to make and receive calls and SMS messages. This comes under the heading of 'Continuity' also known as 'Handoff'. See Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

Note: You need a 2012 or later Mac mini model.

For details on how to setup SMS messaging see http://appleinsider.com/articles/15/04/04/how-to-enable-sms-text-messaging-throu gh-continuity-on-ipad-and-mac

Apple do not provide an easy way to make calls on the Mac via Continuity, the nearest Apple provide might be to open a contact in the Contacts program and it would then dial a call. However this app solves things much more elegantly. See https://itunes.apple.com/us/app/keypad/id928906884?ls=1&mt=12

There is another option as well, WiFi Calling. This is a wireless

provider feature that in a couple ways.

-It lets you make calls from your phone via WiFi instead of cellular.

convenient when cellular is not available.

-Also allows any supported device to make and receive calls via WiFI.

The devices need to be enabled.

-The other thing with additional devices, with WiFi calling enabled, the phone

does not need to be nearby, on WiFi, or even turned on for that matter.

Make a call with Wi-Fi Calling - Apple Support

I do, can, using Gmail & my Google Voice (Hangouts). Bought this cool little stand up MIC from amazon, and it stands on top of it. Have a headset nearby, and when I call it is clear as a bell, but to receive calls, I'd have to leave the Mini on. I primarily use it to make call, like to family in Germany, having bought myself credits, my calls to Germany just 2 cents per minute.

OS X El Capitan: Use your Mac to make and receive phone calls

Facetime, look at its preferences. You must sign in with Apple ID on that Mini.