I fixed!!! Just when I submitted my last post I found the solution xD
I went to the ios-sim project on github: https://github.com/phonegap/ios-sim and they said the ios-sim supports xcode 6.x only for version 3.x, my version was really old (1.9.0), you just need to update and that’s it!
$ npm uninstall ios-sim -g
$ npm install ios-sim -g
There you go! The simulator should work now from your Ionic project.
$ ionic emulate ios
Regards