1. Mac with Yosemite installed.
2. iPhone with IOS 8 or above.
3. Both your Mac and iPhone are connected to the same wireless network.
4. Both devices are signed in with the same iCloud account.
5. Both devices are bluetooth turned on.
If you have satisfied all above conditions, you can make your phone call in you Mac......
But how ??
There is no dial pad in Yosemite, right ?
Here are the situations to make phone calls in Yosemite:
1. Click the phone icon in a contact's details within the Contacts app
2. Click the phone icon next to a valid phone number detected by Safari
3. Manually select a phone number and right-click it to call through a context menu