Blocking Robo/Spam calls

[The Duke]

I get about 20-30 robo/spam calls a day. I've got Verizon and using their call blocker but all it intercepts is the ones already known as spam.
How can I automatically send all calls to voicemail that aren't in my contacts?

I need the unknown callers to come thru for my business.

 

[member160292]

Robokiller $40 a year
Call screening for those not on your contact list

 

[Kotaix]

Verizon has a caller screening service. My gf uses it, but I don't know much more since I don't have Verizon.

 

[Billtx49]

I use Hiya on my iPhone. Very happy with the spam blocking results.

 

[RickTheToad]

I use nomorerobo.