cell phone + computer lab = no

Why do so many people answer their cell phones in quiet computer labs full of people trying to work, and keep a conversation going? It seems to me that there are three options:
1. Don't answer.
2. Answer, talk QUIETLY and end the call within 90 seconds or less.
3. Leave the room to talk on your phone.

Absolutely DO NOT:
-Gossip loudly
-say "...oh nothing much, I'm just in the computer lab" and continue talking.
-plan your evening at length.

I've been in a computer lab a few times lately when people get phone calls. One where the girl LOUDLY gossipped and made arrangements to meet a friend. That's nice, but I'm here to work. You may have paid for your phone and a phone plan, but I came to this QUIET, internet accessible room to get some work done. I have so far managed to NOT say anything, but one of these times, I'm going to just tell someone to shut up.