Musix gets an update and now also supports the iPhone! Excellent news! As well, you can now just drag the keyboard around on screen to change what range of notes are shown.
If you didn’t catch the details of some of the previous releases, the developer also added additional Midi and OSC options. There is now the ability to have the note velocity change depending where you strike a note and the ability to do vibrato by wiggling your finger within a note.