You can now make and receive phone calls via OS X. However, you don’t have a great keypad in the operating system with which to do that. While you don’t really need one, assuming you’re calling your contacts, having some kind of keypad makes it super-easy to call everyone else’s numbers.
Keypad for Mac
This $1 app drops a little keypad on your screen that you’d use just as you would the keypad on your iPhone. 
You can click on the numbers, copy and paste them in, or just start typing the name of the person in your contacts list.