Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.Download on the App Store
Audiobus is the app that makes the rest of your setup better.
Taking IOS for a walk, a ride, a hike, a flight, a sky dive?
I'll be honest: I mostly use this iPhone mod'ed guitar rig while on the couch with the TV on using subtitles to follow the story. But I could be the guy that takes a walk and get's hit by a bus.
Using the Headphone port for audio input allows me to connect Battery packs
to the lightning connector for some long sessions. I could velcro the battery to guitar too or put it in my pocket.
I have a similar rig with a battery powered keyboard that has internal speakers
for playing in the garden with it on my lap. I use headphones but I could use the speakers too for a busking rig that fits in a backpack. I should look for a key tar to do the take a hike story to another controller (the iPhone guitar has Guitar to MIDI 2 installed and that's fun).