Panel Switch - Telephone Numbering

Telephone Numbering

As in the SXS system, each installed office could handle up to 10,000 numbered lines, requiring four digits for a line number within the office plus an office code.

The panel system was designed to interconnect the offices of a city or a local calling area. Each office had a two-digit code (later three). Callers dialed the office code followed by the line number within the office. In most situations this led to six-digit numbers (later seven). But from the beginning the panel system handled seven-digit numbers (later eight), for two reasons.

• Party line numbers were listed with a J, M, R, or W following the line number. The caller dialed the office code, the line number, and the digit corresponding to the letter.
• The panel system was designed to work with manual offices of up to 10,500 lines. Callers dialed the office code followed by the line number within the office. For lines 10,000 and up, callers therefore dialed the office code and a five-digit line number.