Bluetooth on Subway

I live in New York City where over a majority of the subway routes are underground. There is also no cell service down in the subway--unlike Paris's Metro in which you get service on the underground train. So my question is why do people wear there bluetooth on the subway? It greatly irritates me because its not like that they are going to get a phone call or any thing on the subway. At this point I like to point out that I am typing this up on my Blackberry on the E train heading towards Queens.

I will like to know why people do this and if they do this in other subway system's.

JGold

Sent from my Verizon Wireless BlackBerry