If people are interested in this type of thing for Android, I recommend checking out the RedPhone and TextSecure apps.
They're free to use, all the source code is GPLv3 on GitHub, and RedPhone already has global calling coverage. The apps have been translated into 15 languages, and in my experience they're really dead simple to use.
Stop hoping and port it, then. The protocol[0] is based on OTR, which already has at least one Cocoa implementation in Adium. AFAIK you can't directly tap into SMS on iOS, so you'll either need to do a lot of copy/pasting or run across your own messaging network.
They're free to use, all the source code is GPLv3 on GitHub, and RedPhone already has global calling coverage. The apps have been translated into 15 languages, and in my experience they're really dead simple to use.