ring, ring

I went to the SF Symphony on friday night. During the crucial (and of course, dead soft) part of the piece, some one's cell phone rang. $%^**#&, !@#$, %$#$*(#)!*&#@!@#(&%#(*$&!@*&#^@#&^!@#$%!!!!!! The conductor stopped, composed himself and the musicians, and started over.

My question is, why do people even bring their damn cell phones into the building in the first place?