make ringtone
i made a ringtone i made called "silent" which is "duh" without sound.
i use this as my DEFAULT ringtone, and assign a normal ringtone to my contacts no more annoying phone calls from people i don't know, telemarketers, bill collectors, wrong numbers, ex-wife/girl, blocked/unknown numbers, etc.
they just get my voicemail that says "i will call you back if i am moved to do so by your message and i also have your number"
when you wake up you can change your default ringtone back to normal.