How does a cell phone change the
incoming signals from a caller into sound that
you can hear

they send electrical signals to the buzzer. The buzzer changes those electrical signals into sound. You hear the buzzer sound and know that someone is calling you.

Explanation:

Cell phone or any electric device you can say changes the electric signal to radio waves at transmitting end which is converted back to electric signal and perceived as sound waves at receiving end

Explanation:

(http) hyper text transfer protocol

which means its an input that allows the "site" to connect with severs.