RoboKiller is a call-blocking service that bills customers $25 per year and can be canceled anytime. It listens to incoming spam calls on one's cell phone, including robocalls and telemarketers. Their Answer Bots answer the spam for the user, while also updating their block list in real-time. RoboKiller estimates about a 90% spam reduction for customers within a month. The Answer Bots detect voice patterns while trolling the spammers themselves via fake vocal answers. You can even sample some instances on their website. Robokiller also features personalized "allow" lists for callers you want to let through. Robokiller has a 7-day free trial and is available on iOS & Android.