Though cancelling a shoot at the last minute is generally not a professional thing to do, there are times when it becomes necessary. (inclement weather, death in the family, illness, car trouble, etc..)

In those cases, here are my suggestions on how to handle it:

1.)  If the photographer/model has given you a contact phone number (and generally they will) USE IT.  Calling their cell phone (if they have one) is the best way to get them in a hurry, If you get their voice mail LEAVE A MESSAGE but keep trying till you get them.

2.)  DO NOT UNDER ANY CIRCUMSTANCES send an e-mail and leave it at that.  If the photographer/model is traveling a long way they might not have access to e-mail where they are.

Traveling long distances is expensive and time consuming.  If you are asking a photographer or a model to travel a long way, it is appropriate to make sure they know you can't keep the appointment BEFORE THEY LEAVE. 

Please be respectful and if they ask you to contact you a certain way (cell phone, home phone, etc)  PLEASE do so.  The one or two bucks you spend calling them could save them a lot of time, expense, and hard feelings.  It will also make them feel more inclined to be understanding of your situation.

Post 1 million bulletins on myspace and hope someone responds.  lolz