I have the most recent Macbook Pro 13" and on the apple website it says that the audio port is in and out. I just ordered a headset that has two separate 3.5mm plugs and was wondering if there is any sort of adapter that would let me use both the headphone and the mic, or if it has to be one or the other, since there is only one port.
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.