I have an iPhone 4s currently upgraded to iOS 6. iMessage is only working with the apple id. I cannot get it working with my phone number. I had this issue when I was using iOS 5 as well. I think my phone is manufactured for the chinese market or something. I did not buy it from a network. Does this have something to do with iMessage activation? in the iMessage section in settings, it says activation is unsuccessful. But still it says i can be reached with my apple ID.