The Apple Communications Toolbox Modem tool always sends an ATZ (soft reset ) to the modem. The Avatex 1200 Modem chokes whenever you send it an ATZ so use the Serial tool to establish your modem type connection. This tool assumes nothing about the modem and allows the user to type their own AT commands thus enabling them to avoid the dreaded ATZ. The Avatex 1200 modem is the only modem in the world that seems to have this behavior.