At present, it is impossible to play audio, or input audio, in a web page on the iPhone. You can play a linked audio/video file, as long as it is embedded in a .mov or .mp4 container, but that is simply doing playback, not even 'interactive' playback. (It's more like the way HD trailers play from Apple's website. It loads QuickTime Player, they don't play in-browser.)
And as far as I can tell, there is *NO* capability to input audio.
If we get Flash or Java in an update, then you could do it. But not now.