Give cell phones a break...

I've heard a lot of people complaining about loud cell phone users lately. They don't like hearing other people's cell phone conversations on the bus, in a store, etc. One group of people have even organized a movement against it. My question is: why?

What's the difference between somebody having a personal conversation about "the game" or "last night" on their cell phone, and somebody else having it with their buddy (who happens to be there)? One's the most annoying thing in the world, and the other's normal? I don't get it. Somebody enlighten me.

(I understand it's a different thing if people are loud and obnoxious on their cell phone - but it's the same as if they were being loud and obnoxious with somebody physically there. Both are annoying. But if they're just talking normally, as they would with somebody that was there, then I don't see the point of making a big deal about it.)