Ooh. We've actually had clients DO this..

They call up, confused because they got a bill from the local 911 provider for making 1000+ calls to 911.

(Seems that the manager who set up their system was under the impression that they had to hit '9' to get an outside line. Like their PBX. Add that to the 1 country code, and mis-loading a WHOLE BUNCH of exchanges gave them a calling list of 32k+ "911..." numbers.) Oops. It actually did cause us to implement a small check. if the first three digits (even for, say, a valid number) turns out to be 911, then dump the number...

Me.