Try pulling out your phone and dialing *72 followed by another number. It will forward your device calls to the number you dial.

That's the key here. You forward your device number to CallStop, which uses VOIP Pushkit to receive calls. In that way, each CallStop user can set code level rules on who can reach them and when. It's like a firewall for phone calls.

Here's a sample number you can call to try this out: 650-300-0574

You should be able to get a good idea of how the service works by selecting different options when calling it. Try pressing 1 and check out the text you get to add a whitelisting note, or 2 and try entering a PIN. CallStop users get push notifications for whitelist requests and rejected calls.

One of the cool implications if a service like this is adopted is that phone numbers for anyone can be public and it will no longer matter.