Fax machines and analogue devices

Last reviewed: 2026-03-04

Why fax machines are affected

Fax machines send documents as audio tones over the phone line using a protocol called T.30. This works on the traditional analogue network (the PSTN) because the signal travels as a continuous sound from one end to the other.

Digital voice does not carry sound the same way. It compresses and decompresses audio in a way that is designed for human speech, not for the precise tones a fax machine needs. The result: fax transmissions over digital voice lines are unreliable. Some may get through. Others will fail partway, produce garbled pages, or not connect at all.

According to Ofcom's guidance on landline services, devices that rely on analogue signalling may not work after the move to digital voice.

What happens after the switch

Once your phone line has been moved to digital voice, a fax machine plugged into it may:

• Fail to connect to the receiving machine
• Connect but produce unreadable or partial pages
• Work intermittently, sometimes fine, sometimes not

There is no fix that makes traditional fax reliable over digital voice. The underlying technology is incompatible.

Alternatives to a phone-line fax machine

If you still need to send or receive fax, you have a few options:

• Online fax services. These let you send and receive faxes through a website or app. You get a fax number, and incoming faxes arrive as email attachments (usually PDFs). No phone line needed.
• Fax-to-email. Some phone providers offer this as an add-on. Incoming faxes are converted to email. Outgoing faxes are sent from your email or a web form.
• Email or secure file transfer. If the person you are faxing agrees, you can send documents by email or through a secure document-sharing service instead. For most everyday uses, this is the simplest replacement.
• Analogue telephone adaptor (ATA). Your phone provider may supply an ATA box that lets you plug in analogue devices. Fax over an ATA is still unreliable because the digital compression problem remains, but some people report limited success for occasional use. Do not rely on this for anything time-sensitive.

Fax in medical and legal settings

Some GP surgeries, hospitals, pharmacies, and solicitors still use fax for sending prescriptions, referral letters, or signed legal documents. In some NHS workflows, fax has been the default for years.

The NHS has been moving away from fax, but some services still depend on it. If you run or work in a practice that sends faxes, check with your IT team or clinical commissioning group about approved alternatives. Most NHS trusts now accept secure email (NHSmail) for the same purpose.

Solicitors who use fax for exchange of contracts or signed documents should check with their practice management system provider. Electronic signatures and secure email are accepted in most conveyancing and litigation workflows.

Other analogue-only devices

Fax machines are the most common, but they are not the only devices that rely on the old phone line. Others include:

• Dial-up modems. Any device that connects to the internet by dialling a phone number. These are rare now but still exist in some legacy industrial equipment, remote monitoring systems, and older building management systems.
• Franking machines with phone-line connections. Some older models download postage rates by dialling a central server. Most modern franking machines can use broadband or Wi-Fi instead. Contact your supplier.
• Alarm communicators and autodiallers. Covered in detail in our security and fire alarms guide and our monitoring and alarm signalling guide.
• Data loggers and telemetry devices. Some environmental monitoring, utility metering, or industrial control systems use a phone line to send readings. These are typically managed by specialist suppliers who should already have migration plans.

What to do

1. Identify any device that plugs into your phone line. Follow the cable from the phone socket. If something other than a telephone is connected, it may be affected.
2. Contact the device supplier or service provider. Ask whether the device works over digital voice. If not, ask about replacements or alternative connection methods.
3. Ask your phone provider about an ATA. If you are told one will be supplied, ask specifically whether fax or data transmission is supported through it. Get a clear answer, not a vague "it should work".
4. Test after migration. Once your line moves to digital voice, test every device. Do not wait for something to fail in use.
5. For medical or legal fax use, check your sector's guidance. Do not assume your current workflow will survive the switch. Plan the replacement now, while you still have time.