For this cable using colored cables for immediate visual distinction, pink for microphone (line in) and green for loudspeaker (line out). http://www.ebay.com/itm/Stereo-Audio-Aux-Headphone-Cable-Extension-Cord-for-iPhone-iPod-MP3-3-5MM-TR99-/231379408016?var=&hash=item35df499490
Ι  use stereo cables which in this case I have shorted the left and right channel. Beware these cables are very thin and need attention to their welding. To remove the insulating varnish, use flame.

For the connection use the diagram below: