A few references:
Classic PGmidi (Pete Goodliffe)
http://goodliffe.blogspot.com/2010/10/using-coremidi-in-ios-example.html
The synthetic bits coreMidi braindump is now password protected… sigh
A helpful diagram showing terminology
http://xmidi.com/blog/how-to-access-midi-devices-with-coremidi/
Useful core Audio and core Midi links for iOS
http://www.deluge.co/?q=core-midi-core-audio-useful-links
an older ios midi project
https://github.com/JohnGoodstadt/MidiNotes