I have to go back a bit because in order to understand the concept you have to look at what was laid out in previous devices. The iPhone imo is basically a mobile computer. Apple, in the past, has stated that their Applications/Software works together. If you are familiar with Microsoft Office? Whenever you needed to use an address in Word, you had to take 3-4 steps to import an address into the letter you were composing. In Pages, Address Book is easily accessed because it was incorporated in the app (versus importing). When comparing the computer's functionality, it's the same on the iPhone. Again with computers
This is the same as creating a Database (Contacts) which you export to another application. The export function is already complete so you don't have to do that.
So back to the phone. Instead of importing the Contacts information, FaceTime and Phone have the Contacts installed within the app. The same with Mail. Remember you are not saving any info in Phone, Mail, etc.. everything is saved in Contacts aka Address Book.
I mention iOS 6 because it looks like Apple did not update the app when ios7 came out. It would be a lot cleaner if Apple would only list what is needed in FaceTime, phone numbers and emails. When you open the FaceTime app on your Mac, only the phone numbers and emails have been exported from the Address Book.
At one time in Address Book, you could make call from the Address Book app on your computer. You would click on a phone number inside Address Book, that number was sent via bluetooth to your cellphone to make the call. Basically that is what you are doing now on your Phone.

I wish they would bring that feature back. Its good to have if you work from home or use your computer for business.
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