I've stopped answering my phone completely unless the number is in my contacts. If I plan to communicate with anyone (recruiters, etc.) I make it explicit that I won't answer their call unless they give me the number they'll be calling from ahead of time, and then I tell them I'll place them in my contacts with that number.

My hope is that this is training these individuals to be more aware of the issue, assuming they've forgotten about it due to being desensitized or using some paid caller ID spam service that not everyone has access to for lack of funds.

I've also long turned off my voice mail; it's just a waste of time.