Dabbsy has one detail wrong.
I live in northern France, near the border with [REDACTED](1), and I have to say, having watched people around me, that he has one important bit wrong in his analysis of people using the ends of the phone.
There are many around me who speak into the end where the speaker is, with the microphone pointing away from them, and then switch ends to listen to the microphone.
(It is sometimes not obvious, but sometimes they hold the phone far enough away from horizontal that the home button can be clearly seen on the end away from their mouth when they speak, and/or on the end near their ear when they listen.)
(1) Douglas Adams assured me that the name of this other country is, in fact, a very rude word, so I thought it would be polite to spare your collective blushes.