I've just ordered a microphone for my Pc, and I was just wondering what would happen if I plugged it in my iPhone headphone jack. I fear it might break the microphone, or would the iPhone recognize it as a microphone and "use" it properly?
Nothing will happen. Hopefully. The drive and source signals are as different as night and day. The mic input has a dedicated IC and is normally expecting a condenser mic.
It may also output a 1.5 VDC 'shadow' voltage to drive the mic. The headphone output is another dedicated IC with a stereo output of just a couple of volts. Software does not read these input/outputs because they are dedicated to their functions.
Some headphone outputs have a 4 wire plug so plugging a mic into it could short or overheat the headphone driver IC. Not sure what your trying to accomplish by doing this.