I assigned ringtones to everybody in my contact lists as wife, business, family, utilities, Credit Cards and others. Then I assigned "no ring" as my  regular ringtone, so my phone is silent when I get a call not in my contact list. If they do not leave a message, they are just a call I delete every few days from my missed call list. If they do leave a message or one that is incomplete as to full name, who they represent, phone number and why they are calling, I delete the number and do not call back. I no longer need to block calls. This unknown caller hung up, left no message. I never knew they called until the end of the day when I cleared my "missed call" log.