How can I use my Apple earbud mic with the internal speakers on my Macbook Air? When I plug my iPhone headset into my Macbook Air, the operating system recognizes both the headphones and the microphone. As a "side-effect" it disables the internal speaker and microphone.

Is there a way that it only disables the internal mic, but keeps the internal speakers functioning? What I would like to achieve is that the sound coming in from the external mic is played over the internal speakers. LineIn doesn't help me (yet), because the internal speaker gets disabled.
You can solve this problem physically with an extension cable.

Check the tip of the extension cable (the male end) for the number of rings. If it only has 2, it is only recognized as a pair of headphones. The third ring carries microphone audio which you'll see on the end of the headset cable.