Wasn't Apple's iMessage protocol supposed to be an open implementation too? Whatever happened to that?
That was FaceTime that they intended to open source, and it was supposedly a patent troll that forced them to move FaceTime to a more centralized design (it was originally P2P) which in turn made open sourcing more problematic.
That was certainly the excuse. But it is trivial for Apple to buy any patent it needs. I believe the real reason is that FaceTime and iMessage hook people to Apple platform and discourage switching to another one.