Macworld head honcho Jason Snell got his hands on a pre-release version of the Shure Music Phone Adapter
(MPA) and has an enthusiastic preview
over at Macworld. The MPA is basically a microphone that plugs into the iPhone to allow you to use non-Apple headphones to make calls. Most importantly it allows you to use canal-phones (like those from Shure, Etymotics, and Ultimate Ears among others) with your new favorite toy.
Having used a pair of Etymotics for the past few years I can't imagine going back to earbuds, so a device like this would be a must for me. Further, since most headphones require an adapter for use with the iPhone anyway (given the strange port design), the Music Phone Adapter looks to be a very useful accessory. It is "coming soon" for $49.95.
[via Macworld iPhone Central