When I had my iPhone 5 I had the same problem, it was solved by just reset and roll back to old backup that had imessage and FaceTime activated with my phone number; when I got my 6 plus everything was OK doing it like that.
My wife had a 4s that at some point she was unable to activate the services, right now she have a 5s and till this day it's impossible for her active the services with her phone number but she can using her apple ID.
The number have never showed....
If you have a backup I suggest give it a try.