I know that Clark has used ooma in the past and we do too. Its a device for VoIP for about $150 one time. You just pay taxes on the calls ($3-4 a month). Their premium level for about $10 a month allows you to not only block specific numbers but those starting with a scammer area code or prefix (first three numbers of a phone number). I find it invaluable.
Meanwhile keeping them from bothering some one else! 
Clark’s advice: If you haven’t already added your phone number to the National Do Not Call Registry, do it. It won’t prevent spam calls but adds your name to a “do not call” list for sales and marketing calls, so it will help cut down on those types of calls."
No, the National Do Not Call Registry (Database #1) does not cut down on ANY calls, landline or cell phone. It appears to be designed for the exact opposite: to provide a ready-made US database of valid names and phone numbers to telemarketers, scammers and other organizations.
The Do Not Call Registry also has another, not-talked-about database (Database #2) of all the telemarketers, politicians, and other businesses that sign up to get access to the stored phone numbers. That is supposed to be so they can avoid calling the numbers. But there is no enforcement actions, and nothing is done if some of the entities on Database 2 do call some (or all) of the numbers on Database 1. What do you suppose happens?
There is no method provided on the National Do Not Call Registry to REMOVE your name from the registry. Once on there, it stays there forever, as far as I can tell. If you have not yet fell for this government-sponsored scam, then think twice before you put you name on the un-erasable list.
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