The electronic circuit network used in Vikingft. s Hot Line phones * 0 to 20 digits* Installs into 500 554 2500 2554 standard phones * E(2) nonvolatile memory. For CO Centres or PABX loop start lines * Blocks hand-held dialers or pulse dial. * Converts phone to one number Touch Tone or rotary auto dialer when handset lifted. No batteries required