i had a similar idea (don't know if i understand yours correctly), of using android as a line-in audio recorder. then i found out android can use external usb cards. then i got a cheap behringer usb audio interface (48khz/16bit stereo) and made a adapter to slide in the phone and use it as recording device.
not studio quality, but good enough for most recording needs (before i got my DR-70D).
for mic thou would need a preamp. or could use the internal op-amp from the interface (i removed from my behringer to make it smaller) and make it have gain instead of being a buffer.
its also good to use as RTA (the input is very linear)
EDIT: i was wondering how it could record stereo from the audio jack (on sony's phones), that have only 4 connections, but realized that there is audio mics for sony phones that sony itself make, that have 5 connections on the jack, to make stereo "in" possible.
depending of the input preamps i believe can be useable. also, if have any manual gain adjustment, better yet, so you can lower them and use better external preamps (like people do with DSLR crappy internal preamp, but i believe even in the minimal gain would be too sensitive, may need a attenuator)
https://www.youtube.com/watch?v=HCAaD6xMDFk