Amazon.com: MillSO Headset Splitter for 2 TRRS Headphones or Mics 3FT - 3.5mm Jack Adapter TRRS 4-Pole Splitter Male to Dual Female Adapter Compatible for 2 Headsets, Microphones to Mobile Phone, Laptop -
Cell-phone TRRS Headset - Earbud Headphones w/ Microphone : ID 1966 : $3.95 : Adafruit Industries, Unique & fun DIY electronics and kits