Ubiquitous Product of the Week The TeleZapper ($49.95) What Is It? The hot-selling gizmo that wards off calls from telemarketers. How It Works By emitting a tone that makes computers think the line is disconnected, the Zapper deflects computer-dialed calls so the pitchperson never gets through. ”When there’s no one on the other end, you know you’ve zapped them,” says a product rep. But Hold On…Detractors claim the gadget also disconnects important computer calls, like from the police. ”The best way to screen calls,” huffs a spokesman for the American Teleservices Association, ”is caller ID.” But that’s another infomercial.