Retrobilly tries to output some 16000hz wave files.
Quote from PoorAussie:
I spent a few hours tonight putting together a small (no pun intended) ROM which tries to output some 16000hz wave files. It works fairly well, except for some "noise" I am finding hard to get rid of, likely related to the non linear distribution of the SMS channels. . It uses two square channels and some preprocessing to get it into a SMS format that is adequate. 3 Squares might help get rid of some of the noise, but I found that small delays between each square channel adds its own distortions.