I kind of passed over this when I saw it earlier in the week, just because I don't have the necessary phone, but Syntrax looks amazing - 8 stereo channels, sample playback, a soft synth, a sample editor (!), realtime filters etc etc. ON A MOBILE PHONE! It only costs $20 and was created by Reinier van Vliet, a Dutch programmer who's been doing this kind of thing since Mugician on the Amiga.
Posted by Tom Whitwell. 
