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A key telephone system (KTS) is a phone system that lets multiple telephone lines or services appear on one telephone. The Federal Communications Commission (FCC) defines it as a system that can present more than one telephone line, PBX extension, private line, or intercom line on a single telephone. The definition describes possible line types; it does not mean every installation offers all of them.
What does “key telephone system” mean?
The defining feature is that a user can access multiple line appearances from one telephone. The FCC glossary calls this a “Key System,” also known as a “Com Key System” or a “KSU.” In its FCC 13-100 glossary, the FCC defines it as “a type of phone system that permits more than one telephone line, PBX extension, private line, or intercom line to appear on a single telephone.” FCC 13-100 glossary
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In practice, the telephone is where those lines or services are presented to the user. Which kinds are available depends on the particular system; the definition does not promise that every KTS supports every listed line type.
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How is KTS different from MLTS, PBX, and other terms?
In U.S. law, a key telephone system is one type of multi-line telephone system (MLTS). MLTS is an umbrella category that also includes PBX and hybrid systems, along with network- and premises-based systems such as Centrex and VoIP. The statute names KTS, PBX, and hybrid systems as distinct types within that broader category, so KTS and PBX are not interchangeable terms. 47 U.S.C. § 1471
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AT&T CD4930 Black Corded Phone with Digital Answering System, Caller ID, Extra-Large Tilt Backlit Display & Big Buttons
- 25-Minute Digital Answering System — Never miss a message again. Record up to 25 minutes of incoming calls, outgoing announcements, and memos with easy instant playback, selective save/delete, and the ability to skip or repeat messages right from the handset or base
- Extra-Large Tiltable Backlit Display — See Caller ID names, numbers, time, and date at a glance — even Call Waiting. The oversized LCD tilts for the perfect viewing angle, reducing strain for seniors and anyone with vision needs
- Oversized Big Buttons — Large, high-contrast keys are easy to read and press — ideal for elderly users, arthritis, or low vision. Simple, frustration-free dialing every time
- Hands-Free Speakerphone — Talk and listen comfortably without holding the handset. Perfect for multitasking, note-taking, or including the whole family in the conversation
- Reliable Corded Design with Audio Assist — Works even during power outages. Audio Assist temporarily boosts volume and clarity for better hearing, plus an extra-loud ringer with visual flashing indicator
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Panasonic Cordless Phone, 2 Handsets Link2Cell, Landline Phone for Home
- Phone System with Corded Base Unit + 2 Cordless Handsets: Enjoy the clarity of corded landline phone calls with the flexibility of using the cordless office phones anywhere in the home or office; add cordless handsets (sold separately) to grow your system
- Large Phone Base; Large tiltable 3.4-inch LCD display of the corded house phone gives a clear reading of who's calling, with one-touch dial buttons for frequently dialed numbers; a big red call block button makes it easy to block nuisance calls
- Hands-Free Phone Functions that Simplify Your Life: Hear caller announcements in English or Spanish with Taking Caller ID; full duplex speakerphone lets you use your desk phone handset hands-free on this home phone and even answer calls by voice command
- Advanced Call Blocking: Panasonic cordless phone Automated Call Block pre-blocks robocalls. Telemarketing Call Block lets you block announced callers; block 1K more with 1-touch Call Block Button
- Record Your Calls: 2-Way Call Recording with this business phone helps you never miss an important detail in business conversations to confirm what was said and avoid mistakes; the Recording Start button makes it easy and deters nuisance calls
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Uvital Corded Phone for Landline, Black LCD Telephone Landline Phones
- [LCD Display] Uvital corded phone features an LCD display with caller ID, 5 levels adjustable easy-to-read numbers, stores 61 incoming and 16 outgoing calls, and supports date/time. Note:Caller Name Not Displayed
- [Ringer Volume] The landline phone has a loud ringer up to 110 dB with High-Low-Off settings. The phone includes a red LED visual indicator that lights up for incoming calls, ensuring you never miss important calls. Note: Lights only for incoming
- [Hands Free] Our telephone provides hands-free calling with a speaker reaching up to 90 dB. It includes 2 levels of adjustable speaker volume for greater convenience
- [Multi Function] The desktop telephone supports one-touch and two-touch memory, along with dedicated FLASH, MUTE, and REDIAL buttons, integrating multiple functions for efficient operation
- [No Battery or Power Required] Simply plug in the RJ11 phone line to start using it—no batteries or external power source required
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VTECH VG208 DECT 6.0 Corded/Cordless Phone for Home with Answering Machine, Call Blocking, Caller ID, Large Backlit Display, Duplex Speakerphone, Intercom, Line-Power, Expandable to 5HS (Silver/Black)
- Hybrid Corded Base Plus Cordless Handset: Combines a reliable corded base that works during power outages in Line-Power mode with the mobility of one DECT 6.0 cordless handset for home or office use
- 22-Minute Digital Answering Machine: Records up to 22 minutes of incoming messages, outgoing announcements, and memos with easy access and management from the base, handset, or remotely
- Advanced Call Blocking: Blocks unwanted calls from robocallers and telemarketers by saving up to 150 names and numbers directly from the handset or base for a quieter home environment
- Large Backlit Displays and Easy Buttons: Features extra-large 3.5-inch backlit base display and 2-inch handset screen with high-contrast text for clear Caller ID viewing, plus lighted keypad and big buttons for simple dialing
- Full-Duplex Speakerphone on Base and Handset: Enables natural, hands-free conversations without cutting in or out on both the base unit and cordless handset for multitasking and family calls
#1 Best Overall
AT&T CL2940 Corded Phone with Speakerphone, Extra-Large Buttons and Tilt Display, Caller ID/Call Waiting, Audio Assist Volume Boost, Black
- Senior-Friendly Big Buttons & Display: Extra-large buttons and a tiltable display make dialing and reading easy for seniors or anyone with vision challenges — no more squinting or misdials.
- Hands-Free Speakerphone: Enjoy clear conversations without holding the receiver; perfect for multitasking or group calls at home.
- Audio Assist Volume Boost: Amplifies incoming sound for easier hearing — great for users with hearing difficulties.
- Reliable Corded Operation: Works without AC power for basic calls during outages or emergencies; Caller ID requires 4 AA batteries (not included).
- Caller ID and Call Waiting: See incoming caller names and numbers on the large display with a 50-name/number history for effective call screening.
| Term | Meaning in this context |
|---|---|
| Key telephone system (KTS) | A system that permits multiple lines or services to appear on one telephone. FCC 13-100 glossary |
| Multi-line telephone system (MLTS) | The broader U.S. statutory category that includes KTS, PBX, and hybrid systems, as well as other named system types. 47 U.S.C. § 1471 |
| PBX, hybrid, Centrex, or VoIP | Other system types named in the statutory MLTS definition; the cited sources do not provide a full feature-by-feature comparison with KTS. 47 U.S.C. § 1471 |
What the definition does—and does not—tell you
- It identifies a system category by its ability to present multiple lines or services on one telephone.
- It does not specify a system’s capacity, cost, features, or current availability.
- It does not establish that a particular modern handset will work with a legacy KTS. Compatibility requires checking the handset and the specific system.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
