I picked up the Shure MPA-3C Music Phone Adapter from the Apple store today. The adapter includes a microphone and narrow plug and is compatible with the iPhone. So far I’ve only tested the playback quality and it seems to be on par with the straight through wired connection, so no change there.

Shure MPA-3C Package MPA-3C Adapter Unboxed Shure MPA-3C with Shure E500 Earphones