Unlike similar recording interfaces for iOS, the input of the TASCAM iXZ can be switched between microphone-level or guitar level in. When switched to guitar level, the iXZ doesn't require any power.
Today I tested this device on a iphone 6, worked fine. Really simple to use, just plug and play. Using a dinamic EV hand held the level was good enough. Not tested in other smartphones but I beleive It should work.
I have not found a way to monitor the signal from the microphone when recording, only works when you play the recorded files. I Think this is a major problem.