I use an Android app called Hiya that I think evolved from the old White Pages databases and ended up being a caller ID and more importantly a spam blocker. After researching a number of options I put this in my Android phone two or three years ago and have had far fewer spam calls get through. Usually the phone will ring once then stop because Hiya recognized and blocked the number as one reported for spam or telemarketing. Sometimes it will ring but the message slides across the screen that it is a suspected spammer, so I decline the call. Every so often one comes through, I realize it's a spoofed number or spam, so I report it on the Hiya site through the phone. And on occasion I'll get a message saying "you saved (for example) 457 people from getting spam calls by reporting a number." Since it's usually a robocaller it's easy for them to block that many calls for members once it's reported to the system.

They also have a Facebook page.

All of that said, if a call rings through that I don't recognize, I tend to pause and listen for a moment - if it clicks off - spam. If nothing, I say Hello, and the person on the other end probably has an idea of why I delayed. That happened today with a call from a pharmacy that is new to me but working with my doctor's office.