AT&T System 25 Telephone PBX Cabinet with CPU Memory Service Line Cards

AT&T System 25 Telephone PBX Cabinet with CPU Memory Service Line Cards

The AT&T System 25 is a modular digital private branch exchange (PBX) telephone switching system designed for mid-sized business telecommunications environments. This listing includes two complete cabinet units equipped with a full suite of circuit cards for handling incoming lines, trunks, and system control. The System 25 represents the telephone switching technology of the 1980s-1990s era and was widely deployed in corporate offices, call centers, and telecommunications facilities during that period.

Specifications & What's Included

• System: AT&T System 25 PBX Telephone Switching Cabinet
• Configuration: Two complete cabinet units with modular circuit cards
• Cabinet 1 CPU/Control: ZTN142B CPU/Memory Card
• Cabinet 1 Service Module: ZTN131 Service CKT/T1 Card
• Cabinet 1 ATL Line Cards: ZTN79 V7 ATL Line Card (1 unit), ZTN79 V6 (2 units), ZTN79 V4 (1 unit) — Total 4 units
• Cabinet 1 Tip Ring Cards: ZTN78 V3 Tip Ring Line Card — Quantity 4 units
• Cabinet 1 Loop Start Trunk: ZTN77 V4 Loop Start Trunk Card — Quantity 2 units
• Cabinet 2 ATL Line Cards: ZTN79 V4 (2 units), ZTN79 V8 (1 unit), ZTN79 unversioned (2 units) — Total 5 units
• Cabinet 2 Tip Ring Cards: ZTN78 V7 Tip Ring Line Card — Quantity 2 units
• Cabinet 2 Analog Line Cards: ZTN742 V10 Analog Line Card (1 unit), ZTN742 unversioned (1 unit) — Total 2 units
• Cabinet 2 Loop Start Trunk: ZTN77 V4 Loop Start Trunk Card — present
• Total Installed Cards: 22 modular circuit cards across both cabinets

Applications

The System 25 was designed for office PBX applications, providing call switching, line distribution, trunk connections (T1 and analog), and call feature capabilities typical of business telephone systems. The modular card architecture allowed flexibility in configuring line capacity and trunk connectivity based on customer needs. These systems were standard in enterprise telephone networks, supporting both local and long-distance routing, intercom functionality, and integration with analog and early digital telephone networks. The System 25 operated in the transition period from analog to digital business telecommunications, making it compatible with both traditional telephone infrastructure and early data/T1 transmission systems.