Newtech Telephone Training Adapter Y Splitter for Corded Handset
Allows the use of two handsets on one telephone.  Ideal for telephone marketing training purposes. BlackYes this is designed to plug into the telephone and have two handsets plugged in.  This will work even on digital sets as the signal going to the handset is analog.The plug on the cable is 4P4C, some call it RJ9 or RJ22.