How do Nokia headsets work, and how do we hack them?

My understanding of nokia headsets is limited, except for trying once to put a mic and a speaker directly wired to the phone's intputs. And nothing happening.
And opening it up and finding a small chip amongst all the tiny SMD parts.

Do the headsets have some kind of proprietry chip inside to prevent non-nokia headsets from being used?

How does it work?

WHICH headset ? A bluetooth one ?