Here's two things that have almost eliminated those call.
1. My cell phone provider has a service to automatically block registered telemarketers in their system. They also allow me to block calls that make it through, and add them to my personal list, but also the providers lists for everyone's benefit.
2. For the calls that do get through... my outgoing message has over time got my number removed from their "good numbers" lists.
Here's my outgoing message: seems to work well.
Now I only get perhaps 2-3 calls a month.
Which I promptly block.
