imp builds a list of people that you want to speak with. When those people call, your home phone rings. Simple as that.
Whenever anyone else calls, your phone doesn’t ring. Most calls are from people you don’t know - a scam, a robocall, or a political call. For these callers, imp silently takes a message, and then delivers that message to you on your smartphone. If it is a known bad guy imp just hangs up.