Casting extras involves much more than meets the eye. Contrary to vicious rumors, it is not done by bussing in a couple of hundred people and standing them in a parking lot to be chosen one by one by an over worked first AD. Casting extras is actually done via sophisticated computer databases and telecommunications between casting directors and production companies.

It is a relatively new way of casting extras, only developed within the past couple of decades. Your image and profile is kept on file along with a few thousand other would be actors, and production companies call in requesting specific numbers of specific types. This information is posted daily on a voicemail system, which you then access, listening for calls requesting your type. You are the last link in this method of casting extras, as it is your call to the number on the recording that makes the final connection.

They have obviously not been casting extras this way forever, and the truth is that the original way was more or less a situation where nobody was casting extras until the very last minute before production would begin for that day. Hopeful background actors would more or less convene in crowds outside studio gates, and someone (the precursor to today's casting director) would come out and round up everyone they would be needing for the shoot that day.