n-Track Studio & Marshall London (video)
"Watch how you can use n-Track Studio for Android with the new Marshall London phone to record two tracks at the same time. One of the peculiarities of the Marshall London is that it has two separate audio jacks, that allow plugging in two mics.
In this video we used the standard headset that comes with the phone to record the harmonica, while we used a simple splitter cable to connect the acoustic-electric guitar output to the phone audio input and a set of standard (no mic) headphones as well, so that both players could hear what they've been playing.
On all platforms in which it runs (Windows, Mac, Android and iOS) n-Track Studio always allows to record from as many audio inputs as the audio hardware allows. On Android n-Track supports using external USB audio devices, but with the Marshall London there's no need for external devices to record two simultaneous tracks."