Apple has included HTTP Adaptive Bitrate Streaming in the iPhone OS 3.0, in particular Safari handles this automatically.
I\'d like to play with this in a low cost manne
See this for an open source encoder and segmenter and some other cool stuff :)
http://www.ioncannon.net/programming/452/iphone-http-streaming-with-ffmpeg-and-an-open-source-segmenter/