So far i've been borrowing my wife's ipad to play in amplitube and audio out to audio in on my iPad. I also use my iPhone.
Hard way is too play your backing tracks on another audio device while recording guitar part in amplitube and then audio copy/paste or export audio file and import. A real pain either way.
I long for the day when audiobus is a built in feature to all apps.
Btw, i have several apps and devices from IK Multimedia but I have to say they are behind the times when it comes to playing nice with others (apps and devices).
iPad 2, iPhone 5, Mac Mini
iRig Keys, iRig Mic, iRig guitar, You Rock Guitar (midi guitar) Mobile In Guitar, GarageBand, Alchemy, Sunrizer, Cubasis, Music Studio, Amplitube, Mobile POD, MultiTrack, bs-16i, SampleTank, AudioBus, AmpKit, JamUp XT, G2M
Epiphone Les Paul Special GT
Music For iPad