I do not believe it is possible to send and receive through the 3.5mm jack (if it is, this in new technology that I am unaware of, but there is a LOT of new technology I am unaware of). The 3.5mm jack has three wires: 1) left output, 2) right output, 3) ground. There is no possibility of a mike input.
If you read the ebay description, it is for a 3.5mm stereo
output into a 5 pin din
input. What you are trying to accomplish is a 5 pin din output to a 3.5mm stereo input.
If you look at the ebay diagram, you will see that the 5 pin din uses only three of the pins.
[Because I am posting the photo from the ebay ad, it may dissappear at any time.]

EDIT: After giving this a little more thought, I will slightly retract my above statements. I believe the iphone headset (earplugs) include a controller that can change volume on the iphone and maybe even FF or REV. Obviously, the three wires do more than simply provide stereo output. I still do not believe the three wires can add mike input, but I have been wrong before.