your voice shifts air molecules at the speed of sound only up to the microphone. Then the microphone converts the sound waves into electricity. The electrons shifting in a wire are close to light speed, then the phone (or radio, don't forget walkie talkies etc. predate mobiles) converts the electrical signal in the wire into a radio wave, again very close to the speed of light, which travels to the other phone/cell repeater, and the whole process happens in reverse. Light is far faster than sound as can be observed when lightning strikes and the thunder arrives late.