Withphones
Markus writes – “This miniature, 8-line home telephone exchange (PABX) works with standard telephones and features high-quality, user-friendly progress tones. Connection to telephones is via a two-wire unbalanced loop with a common ground. Only pulse dialling is supported although the exchange could be adapted to use a DTMF tone decoder.” Lots of schematics and photos – [via] Link.

Previously: HOW TO – Use old telephones as an intercom – Link.