Conex Electro-Systems CELLJACK CJ-20 Cell Phone Audio Mixer

Not to be confused with Cell 2 Jack (unrelated product).

Please check features and specs online to confirm this suits your needs, no returns for buyer error.

This one is in very good shape with only typical light surface wear from normal use.  See pics.

This is the cheapest one by far that has been listed or sold here, so if you're looking for one, this is your chance for a good deal!