I saw the strangest thing once with two cell phones that both had an Apple ID on them. When you called the number of one of them, it would call the other one about 10 seconds later from the first phone. I immediately thought this was because of the way Face time associates a phone number with an Apple ID. It was probably trying the second phone since the first one didn’t pick up. Sort of like an automatic hunt group where a number will ring on the next phone in a group of numbers.
So I turned off the Apple ID or “signed out” of the Apple ID on one of the phones. It immediately stopped calling the second phone. So I had the person go to Settings > General > Reset and then Erase all Content and Settings. Then she used her second Apple ID and we called the first phone and no more calls to the second phone.
So this behavior is very confusing for the typical person. It should have been made explicit when a second phone is added to an Apple ID. There should have been a warning that comes up that says “This phone may be called when other phones with this Apple ID have been called.” This was not obvious to the typical person. In addition, many, many people complain that the iTunes and iPhone are complicated. I agree. I work with them everyday and I learn things everyday about them. For a casual user, it is too much.
One of the things that I loved in software programs was the idea of “context aware icons”. That meant that you got an icon for functionality only when you were in a position where you needed that functionality. This is opposite to the Ribbon in Microsoft where they show you everything, and overwhelm the average person. All software should only show you the options that apply in that moment. There should always be an icon for help or troubleshooting that people can click and it can walk you through a wizard of common things that can go wrong. Software is great, but it has always been too complicated for people.