thermotelephone

from The Century Dictionary.

• noun A telephone receiver in which the changes of length, due to change of temperature, of a fine wire through which the currents are made to pass actuate the phonic, diaphragm.
• noun A telephone transmitter in which a red-hot wire forming part of the primary circuit of an induction-coil has its resistance changed by the sound-vibrations, thus inducing currents in the secondary which are sent to line.