ANY speaker can be a microphone, this isn’t news. The vibration of the speaker when noises are being made by something around it is enough to generate its own electricity and that can be used to power a transmitter.
This isn’t something unique to any smart phone, its been around for just less time than the modern speaker system existed.
ROTFLMAO
Where did you study electronics?!?! The micro-currents generated from a speaker moving through the SEMICONDUCTORS of the amplifier circuits that drive it, many of which are going to be DIODEs (read UNIDIRECTIONAL, passing current only one way) will not be sufficient to power any kind of transmitter, once you encounter any form of tuned circuit, ignoring that would be the output of the phone's Audio circuitry or CPU! This is an absurdity. Or are you thinking there is some switching circuitry between the speaker and the CPU and the transmitter that the micro current can bootstrap itself to switch from speaker mode to microphone to transmitter without a CPU being powered on? Yes, an engineer can design a speaker that will double as a microphone, but it will neither be a good speaker, nor a good microphone. . . But an unpowered speaker will never provide the wattage to send a radio signal any appreciable distance. Pardon me while I stop and gasp for breath.