Macbook Pro 13" Audio In/Out Port Adaptor
Any headphone / microphone combination that works with an iPhone will work with the MacBook line as the pin connectors are the same.

As a bonus, the play and volume switches get passed to the OS as well.

There are tons of adapters around if you preferred headset doesn't have the correct mic pins to combine the signals in one plug.

Also - look here for the ground that's already been covered.