- An ATA, or analogue telephone adapter, converts the analogue signal from a standard phone into the digital VoIP format carried over broadband, and back again.
- An ATA is needed when a household keeps an analogue phone but the broadband router has no built-in telephone socket to plug it into.
- Openreach is retiring the analogue PSTN as part of the all-IP migration scheduled to complete in 2027, which is why adapters have become relevant for many households.
- VoIP voice is commonly carried using codecs such as the ITU-T G.711 recommendation, which an ATA uses to packetise the call audio.
- Like any broadband-based phone, a phone behind an ATA needs mains power and a working connection, so it will not operate in a power cut without backup.
An ATA is a small box that converts an analogue phone's signal into VoIP and back, letting an old corded or cordless phone keep working over broadband after the analogue line is withdrawn.
Last reviewed: June 2026
What an ATA does
An analogue telephone adapter sits between an ordinary phone and the broadband network, acting as a translator. A traditional telephone speaks in analogue: a continuously varying electrical signal that represents the rise and fall of a voice. A VoIP service speaks in digital packets sent across the internet. The ATA bridges the two, presenting a familiar phone socket on one side and a network connection on the other, so the phone behaves exactly as it always has while the call actually travels over broadband.
When a call is made, the ATA detects the phone going off-hook, provides the dial tone the phone expects, gathers the dialled digits, and sets up the call over the VoIP service. During the conversation it digitises the outgoing voice into packets and reconstructs the incoming packets into the analogue audio the handset plays. It also recreates the small details an analogue phone relies on, such as the ring voltage that makes the bell sound and the signalling that lights a caller-display unit.
When you need one
The need for an ATA arises when two things are true at once: the household wants to keep using an existing analogue phone, and the broadband router has no telephone socket of its own. Many routers supplied for digital voice services include a phone port, in which case the phone plugs straight in and no separate adapter is required. Where the router lacks that port, or where someone wants to connect a phone in a different room from the router, an ATA fills the gap.
Adapters are also useful for keeping particular pieces of analogue equipment alive, such as a treasured corded phone, a fax machine, or a cordless DECT base station. Because the ATA presents a standard socket, almost anything that expected an analogue line can be connected to it. This is why adapters have become a common talking point as the PSTN is retired and households look for the least disruptive way to carry their existing handsets across to the new network.
How to connect one
Connecting an ATA is usually straightforward. The adapter takes power from the mains and connects to the network, either by an Ethernet cable to the router or, on some models, over Wi-Fi. The analogue phone then plugs into the adapter's telephone socket. The provider supplies the account details the ATA needs to register with the VoIP service, after which the phone has a dial tone and can make and receive calls.
The table below summarises a typical setup and the main limitations to keep in mind.
| Aspect | What to expect | Limitation to note |
|---|---|---|
| Power | Adapter runs from the mains | No service in a power cut without backup |
| Connection | Ethernet to router, phone into adapter | Depends on broadband being up |
| Call quality | Comparable to landline with good broadband | Can degrade if the connection is congested |
| Compatible devices | Corded, cordless base, fax, caller display | Some alarms and telecare need checking first |
Once connected, the everyday experience is meant to be invisible. The phone rings, the dial tone is there, and calls are placed in the usual way. The adapter does its translating quietly in the background, which is the whole point of the device.
Limitations and quality considerations
Two limitations deserve attention. The first is power and resilience. Because the adapter, the router, and the broadband connection all need mains electricity, a phone behind an ATA will not work during a power cut unless a battery backup is fitted to the equipment. This is a genuine change from the old analogue line, which carried its own power and kept a corded phone alive in an outage. Anyone who depends on a landline for emergencies should plan for this.
The second is call quality, which depends on the broadband behind the adapter. Voice is carried in packets using a codec such as the ITU-T G.711 recommendation, and the audio is reconstructed at the far end. On a stable connection the result is comparable to a traditional landline, but on a congested or unreliable broadband line calls can suffer from delay, gaps, or distortion. Specialist equipment such as some alarms, telecare units, and certain fax machines may also behave unpredictably over VoIP, so those should be tested or addressed separately rather than assumed to work through an adapter.
Choosing and positioning an adapter
When an adapter is required rather than a router with a built-in phone port, a few practical points make the difference between a smooth setup and an unreliable one. The first is where the adapter sits in relation to the broadband connection. An ATA that connects to the router by an Ethernet cable generally gives steadier results than one relying on a wireless link, because a wired path is less affected by interference and congestion elsewhere in the home. Positioning the adapter close to the router, and connecting the phone to it with a standard telephone cable, keeps the digital part of the journey short and predictable.
The second point is matching the adapter to what the household actually connects to it. A single-port adapter is enough for one phone, while a household that wants to keep a phone and a separate fax line, or two distinct numbers, may need a two-port unit. It is also worth confirming that the chosen service supports the features the household relies on, such as caller display, call waiting, or the ability to dial the same numbers as before, since these depend on the adapter and the VoIP service working together rather than on the phone alone. Where any medically important alarm or telecare device is in the home, that should be raised with the provider directly rather than left to an off-the-shelf adapter, because such equipment often needs a dedicated migration path of its own.
Frequently Asked Questions
What is an ATA adapter?
An ATA, or analogue telephone adapter, is a small device that converts the analogue signal from a standard phone into the digital VoIP format carried over broadband, and converts incoming digital audio back to analogue. It lets an ordinary phone keep working after the analogue line has been withdrawn.
How does an ATA let me use my old phone with VoIP?
The adapter presents a familiar telephone socket to the phone and a network connection to the router. It supplies the dial tone, ring voltage, and signalling the phone expects, while digitising outgoing voice into packets and reconstructing incoming packets into audio, so the handset behaves as it always did.
Does an ATA affect call quality?
Call quality through an ATA depends mainly on the broadband behind it. On a stable connection the audio is comparable to a traditional landline. On a congested or unreliable connection, calls can suffer delay, gaps, or distortion, because the voice is carried as packets that must arrive reliably.
What ATAs are available in the UK?
A range of analogue telephone adapters is sold in the UK, including standalone units and adapters built into broadband routers supplied for digital voice services. Many providers include a telephone socket on their router, which performs the same function, so a separate adapter is not always needed.
Can I use any phone with an ATA?
Most standard corded and cordless phones, and many fax machines and caller-display units, work through an ATA because it presents a normal analogue socket. Some specialist equipment such as certain alarms and telecare units may not behave reliably over VoIP and should be checked or addressed separately before relying on it.
