wav2caf takes a wav file as input, and outputs an ima4-compressed .caf file suitable for playing on the iphone. For source code, build, and install instructions, download here.
Caveats: This source code expect the wav file to be 22050 Hz and single channel. SOX will convert just about any audio file (e.g. mp3, m4a) to this format with a command such as "sox
There's not much to the source file. wav2caf.c looks a bit like aifc2wav, because that's what I started with, then reversed it, sort of. Good luck. If you make improvements let me know.