Harvesting energy from the environment,is the way to go for future cellphones
They have developed a special way thattakes advantage of tiny vibrations in a phone’s microphone or speaker that occur when a person is talking into a phone.
To transmit speech, the phone uses vibrations from the device’s microphone to encode speech patterns in the reflected signals. To receive speech, it converts encoded radio signals into sound vibrations that that are picked up by the phone’s speaker.
The tech is in its nacent stage , but it is a good start !
In the prototype device, the user presses a button to switch between these two “transmitting” and “listening” modes.