Digital vs. Analog Phone Systems

November 2002

Editor: As digital technology continues to displace analog technology, problems can arise that may not have been foreseen. Here's an article from NVRC News that warns of potential problems with digital phone systems.

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A fact sheet released by the Hearing Speech & Deafness Center in Seattle, WA describes how digital phone technology 'has become the standard for businesses across the country...offering multi-line service combined with extra features such as in-house voice mail systems at a much lower cost than traditional analog technology. Digital phone lines often have more wires than a home phone line, and they are configured differently, which means that traditional analog phones will most often not function when plugged into digital lines.......this also means that there are no universal amplifiers or TTYs for use with digital phone systems.'

The fact sheet goes on to warn that due to differences in the amount of electricity carried in digital phone lines, plugging a digital phone line into a TTY, amplified phone or signaling device can cause serious damage to this equipment and possibly to the phone system itself. It is important to determine whether a phone line is digital or analog before installing assistive equipment.

Most telephone lines in the home will be analog lines that are safe for TTYs, amplified phones and signaling equipment. However, it is not advised to connect any assistive devices to an ISDN line often used for internet service, as this may damage assistive equipment.

DSL service, on the other hand, is analog technology and safe for use with assistive technology.

It is likely that telephone systems in the workplace will be running on digital lines which are not safe for TTYs, amplified phones or signaling equipment, since the majority of businesses use ISDN, PBX or T1 phone systems. Often there are analog ports within the system that can be used with assistive equipment and it is important to confirm the analog status of these ports before attaching any assistive device.

It is becoming more common to find digital phone systems in places of public accommodation such as hotels and hospitals, so it is advisable to ask if the phone systems have been upgraded recently or whether there is an analog phone line.