Exactlty, if it is THAT important, they will leave a message where I can reach them. I too do not take calls from numbers I do not recognize. It is a matter of safety...I used to, had to change my number as a result. So really, it is the safe thing to do.
people have answering machine, if it is a famly or friend they will talk to the machine till someone picks it up. i my kid is in jail, he got himself there he can find away out.