Turtle Beach x31

Does anyone know of an adapter that splits the single input/output jack to work as both at the same time, from two different cords?

That can't be done. The port is either input or output, not both at once.

The solution is to use an external USB sound card such as the Griffin iMic, which has separate input and output ports.

iPhone headphones have four contacts on one plug, matching the four inside the MBP's port. Standard plugs with only three contacts can't work the same way.

I know this is 'solved' but I found it while looking for something else.

I must say that I have wondered about this all myself, and although there are much easier, and more affordable ways of doing this. But, for future reference, you could buy a a/v(composite to phono) cable. Radio shack sells them for around $10. It take all four of the contacts and separates them, allowing you to use each of the contacts individually. From what I understand, not only does the turtle beach headsets, but also the xbox headsets use a different pin-out then normal 4 contact plugs, so using the a/v adapter, you can re-arrange them in the order they go, to use with any other analog cables.

So like i said, not the easiest, and not the most cost effective, because when its all said an done, you will more then like have spent about 20+ in cables and adapters. But it can be done.