Last updated · Written for practice managers and office administrators.
A POTS line is a plain old telephone service line: a traditional analog phone line delivered over a pair of copper wires from the telephone company’s central office to your building. It carries dial tone, voice and modem signals such as fax, and it is powered from the central office, so it works when the lights go out.
How a POTS line works
The copper pair runs from a switch in the carrier’s central office (the “wire center” that serves your address) to a jack on your wall. The switch supplies a low DC voltage, listens for the phone going off-hook, sends dial tone, and connects the call. Everything on the line is analog: voice is an audio signal, and a fax or modem call is audio too, a pair of machines whistling at each other in a pattern the other side decodes. That is why a fax machine can plug straight into a POTS jack and why it cannot plug straight into an internet connection.
POTS line vs VoIP vs online fax, for faxing
| POTS line | VoIP line with adapter | Online fax service | |
|---|---|---|---|
| What is at your office | Copper jack and a fax machine | Internet, an analog adapter and a fax machine | A browser or email client |
| How the fax signal travels | Analog end to end | Converted to packets; needs T.38 or a clean G.711 path | Handled on the provider’s carrier network; you send and receive PDFs |
| Power outage at your office | Line stays up (powered from the central office) | Adapter and machine go dark | Faxes are still received; you read them later |
| Future | Being retired wire center by wire center | Some carrier VoIP products are being discontinued too | Not tied to any line |
| Keeps your number | Yes, until the line is retired | Yes, by porting | Yes, by porting |
Why POTS lines are being retired
Carriers are removing or replacing the copper loops that POTS runs on; 47 CFR § 51.325 defines “copper retirement” as exactly that. Stopping the service itself requires FCC authorization under 47 U.S.C. § 214, and AT&T already holds it for business and residential POTS in 39 wire centers, effective on or after July 14, 2026 (FCC DA 26-459). Carriers have announced multi-year programs beyond those wire centers. The landlines overview explains the stages and the FCC copper retirement rules explain the notices you should expect.
What replaces a POTS line
For equipment that must keep an analog jack, a cellular gateway or a VoIP adapter. For a line whose only job is a fax number, an online fax service that ports the number and delivers faxes to email. The POTS line replacement guide compares the three, and the AT&T discontinuance page explains how to check whether your wire center is already on a list.