Background: Bell and his assistant Charles Sumner Tainter jointly invented a wireless telephone, named a photophone, which allowed for the transmission of both sounds and normal human conversations on a beam of light. Both men later became full associates in the Volta Laboratory Association.
Question: Who did Bell invent the cord-free phone with?
Answer:<extra_id_0>.
<extra_id_0> Charles Sumner Tainter<extra_id_1>