shure mpa-3c works just fine
was going through this thread, and thought i would add my bit.
1] Had an old Shure MPA-3C adapter from my iPhone days. And it worked just fine for calls and music control. With PowerAMP you can also control next/ previous by enabling double/ triple clicks. This was a surprise, since i was under the impression that iPhones used a different wiring schema.
The best part about this adapter is that you can plug your own headphones (have the Shure 535, and with the Voodoo fix, the sound is stellar!)
2] Sort of worked with a HTC headset which came bundled with the HD2. This headset has additional dedicated Next/Previous buttons. Calls worked fine, Play/ Pause worked fine. But Next and Previous buttons end up doing the same - skipping to the Next track!
If I can figure out how to fix it, it will be nice - i don't have to bother with triple clicks and such. However the sound quality is rather mediocre and you can't plug in your own headphones - can't see myself using this for anything other than audiobooks.