How do you connect a wireless headset phone cord to standard stereo/mic jacks?

I need to know how to make a wireless headset function as a wired headset.  At the base of the charging station is a standard phone jack.  I need this phone cord split to where it will plug into the pink/green, audio/mic parts of a modified speaker phone.  There is already an existing cord where this was done, but the person who did it is no longer available.  In addition, they didn't put it on the 2 separate jacks, just one large audio jack.