The barriers to iPhone-to-iPhone communication are quickly dropping away. Yesterday I put together a push-to-talk developer pack in the spirit of "just add water", or in this case, "just add point-to-point data transfer". It includes a sample app and code for recording and playing back audio as well as a record-time limiter that will override any push behavior if a message goes on for too long.
What it needs is the inter-iPhone technology. I throw this kit into the wild. Let's see what comes back.