Have you ever tried the following: While sitting in a train, talk to someone standing outside through the window over a mobile phone.
It's interesting to experience the voice delay which isn't very big, I would say in the order of 250 milliseconds, but quite 'visible' as the lip movement of the person outside and the speech path are not quite synchronous anymore. In a mobile phone call where you don't see the other party this delay usually goes fully unnoticed unless you call someone on the other side of the planet and the delay becomes so long that there are odd silence periods and people start talking simultaneously.
The second interesting effect that can be observed is noise supression. As you know exactly how the background noise sounds outside, its interesting to hear if and how well the mobile outside surpresses the background noise and what effect that has to the talker's voice.