TrapCall, Tracfones and Anonymous Calling
One caveat, though. I once used a Vumber to determine where a particular caller was actually phoning from. When I called their number, I heard "You're calling from..." and my TRUE cell phone number! So, new technology is always being created to invade our privacy, usually in the interest in protecting privacy. In my case, I'm learning to find ways to use technology to achieve my privacy preservation ends. But, we should all be wary.
Finally, I think in the case of a domestic violence victim, using a VoIP phone behind a proxy server AND properly configured hardware firewall may help prevent them. Though VoIP phones are much like Vumber, a virtual phone, the user should have someone else with a properly configured (for privacy) VoIP phone call the stalker at a time when the stalker is not answering their phone and see what happens. ALWAYS be testing the technology to see if you can use it to protect your privacy.