So I'm willing to add my voice as well. There are a couple features in iOS that are not well thought out (IMHO), but also are very poorly documented. Ok, not documented at all. The happy-talk Apple website showing how one person on one phone can Facetime one person on their one phone is happyhappy, but of course isn't how it is for Apple's best customers. I often wonder if the poor (non-existent) documentation of how "simple" but actually complicated features like iMessage and Facetime really work (exactly how they work) reflects the poor understanding within Apple of how the software is actually coded.
So my wish #1 is for Apple to start posting real, complete documentation for those of us with multiple iPhones, multiple iPads, multiple desktop/laptops, and our contacts with this much or more and even non-iOS devices. Apple, we are your best customers. We become your best customers by buying many devices, and we need more than a Mickey Mouse hand waving understanding of how we can control it. I should not have to spend time with a friend turning on and off things to try to reverse engineer how these features are supposed to work. After spending $7-8K on Apple stuff, I should feel this much frustration because I'm doing your job?
All, the feature that is driving us wild is called (in the industry) single-number reach. The concept is quite logical if you're an equipment/system designer. What if someone has a bunch of devices (typically multiple phone numbers... such as a work phone and a mobile phone). Wouldn't it be cool if you could just call one number and both numbers would ring? Single number reach to avoid the drudgery of calling one number, hanging up, calling the other number, hanging up... let me try their home number... etc. So our AppleID is the underlying single number reach.
But that's just one use case. What I call "one-to-many". I want to call from my one device to many.
The real world is even more complicated as there is now audio and video. Someone might have 3 audio numbers (ids), and 3 video ids. What then? Apple has failed (big time) because they designed for a single use case, and then went home in their fancy cars to their big homes feeling satisfied. (sorry, snarky rules today)
My use case is my wife is traveling with her iPhone (she has her own AppleID). When I Facetime her (from one of my devices all registered to my AppleID), her computer and iPad here on this side of the house are bonging away. I can't hear myself think. There appears to be a feature where you can supposedly choose how each device is reached (Settings/Facetime/You Can Be Reached...), but it doesn't work. My wife's iPad only has her iPad email checked. And yet, when I double click on her iPhone email from my iMac Facetime, her iPad still rings.
It appears that the You Can Be Reached list applies across all devices using a single AppleID (and to which are linked a mobile phone number and potentially multiple email... each device we have has its own email). So if I remove (I think) the non-iPad email "Reached" line items, they'll disappear from her iPhone and iMac.
A similar process occurs for iMessage/text and to a lesser extent with email. And then there is the complexity other posters have noted about combining contact information under one Contact header (listing). I could design this and document functionality in a couple days. Apple should be able to as well.