These scammers are auto-trolling for active phone lines. I called their number back anonymously using caller-ID block, and got nothing but an invitation to "leave a message".
I'll just unplug my phone, therefore, I don't have to listen to the phone ring for either the scammer collecting active phone numbers or the idiot who actually buys the numbers and tries to call me. If I need to make a call, I'll just plug it in while in use, and I have at least three different ways for people I know to contact me if they need me. The telephone land line isn't the "only" means of communication I have with those I know.