Why can't I use my iPhone Headphones with my HTC Thunderbolt?
They both may have 3.5mm jacks, but if you look at it you can see the the insulating plastic bands around the metal jack. The problem is that Apple wire these sections of the jack up to different inputs than other manufacturers, so that different sections of the jack carry different signals than normal.

I have heard that as long as you're happy with getting mono rather than stereo sound out of the speakers, then you can get the microphone to work by pulling the jack out of the socket slightly. RIM used to do the same thing with their 3.5mm jacks on Blackberrys, but I believe they use the same configuration as most manufacturers (except Apple) now.