Does FaceTime audio call use the Apple ID instead of email address or phone number?

Question

My wife and I each have our own iphones.  The Facetime audio calls come through OK for each one of us, as the calls are set to be received on each of our own email address and phone numbers (so there is no issue here).  But when Facetime audio calls come through, both phones ring at the same time.  I am guessing the FT audio calls (unlike the video calls) are using the Apple ID which is the same for both our phones.  Is this the case?  And if so, is the only fix, to set the phones on different ID's?  Why are audio and video calls set up differently?

Answer 1

It depends upon the device that they are on - from http://support.apple.com/kb/HT4319
To call someone using FaceTime, you need their phone number or email address. Which one you use is determined by the device you are calling:
When calling someone using an iPhone 4 or later: Try the phone number of the person you are calling first. If the person has registered an email with FaceTime, you can use that as well.
When calling someone using an iPad 2, iPod touch, or FaceTime for Mac: Use the email address designated for FaceTime of the person you are calling.
On iPad 2, iPod touch, and FaceTime for Mac, you need to add a person as a contact using the FaceTime or Contacts app before you can call them.