Update: iPhone SDk 3.0 now addresses the question here, however the NDA prevents any in depth discussion. Log in to the iPhone Dev Center if you need more info.
Ok
http://blog.cloudmade.com/2009/06/12/how-to-get-forward-geocoding-in-iphone-mapkit/
CloudMade seems to be an open-source map/location provider - the above blog post lists details on how to get forward geocoding.