I was thinking about business continuity the other day and was wondering how PIN Messaging or even BES Email would work during times of extreme network (I would say both cell and data) usage? For example if a major incident like 9/11 were to occur you can pretty much write off cell phone usage unless you are a big wig in the government, but for businesses would PIN messaging or email usage still be an effective tool to use or would it succumb to the same network issues?

PIN messaging is the most effective on blackberry.
Next is emails on BES, when both sender and recipient are on the same BES.
Next is emailing on BES.
Last is BIS.

Blackberry will try to push message through as long as it has even small chance to do it. The network is not limitless so if it is 100% utilized no luck but if there is even small drop below 100% blackberry will push messages and receive them.

Had not been unlucky to be near twin towers on 9/11, but once was at major accident on highway with cars lined for miles, any attempt to make cell phone call ended with busy signal- everyone tried to call. Emails went through, so I used blackberry to email my office back and forth while my car was standing on highway.

I read somewhere that on 9-11 people with BB's were still able to use them with no problems. Can't say that would ever happen again, but knowing that makes me feel good.

Yes, that's true. And during the big New York City power failure, PIN messaging was also the only effective way to send or receive messages.

This was due to the network. Around 9/11 it was mobitex and datatac.. Since the usual suspects now run on the same networks as the phone network it would be affected the same as cell phones.