Record audio into MP3 on the phone

[alpha752]

I dont know if this is even possible hardware wise, but I was looking for a way to record audio and save it as mp3 on my iPhone. The caveat is I dont want to record via the mic, I would like to use a line in. Is there a way to record through the headphone jack or something similar? Doesnt have to be super audio, mono 64kps is all that really necessary, its just voice im looking to record.