Key takeaways
VoIP (Voice over Internet Protocol) delivers telephone calls as digital data over a broadband connection rather than over copper telephone wires. It is replacing the PSTN as the UK's standard landline technology.
For most users the experience is identical to a traditional landline: same phone handset, same number, same dialling. The difference is that the phone plugs into a broadband router rather than a wall phone socket.
VoIP call quality is typically equal to or better than PSTN. Most VoIP services support HD voice quality and features such as call divert, voicemail and caller ID.
The main limitations are dependency on broadband (if broadband goes down, so does the VoIP phone) and dependency on mains power (VoIP phones do not work in power cuts without battery backup).
All major UK providers now offer VoIP landline services and are migrating customers as part of the PSTN switch-off process.
Reviewed: June 2026Key facts
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How VoIP works
When you make a call on a VoIP phone, your voice is digitised and sent as data packets over your broadband connection to the recipient's phone. The process is the same technology as video calls on smartphones, but optimised for voice quality and reliability. The conversion from voice to data packets and back happens in milliseconds and is transparent to the caller.
Your VoIP phone connects to a socket on your broadband router (the Analogue Telephone Adapter or ATA port, or sometimes via a separate adapter). The router sends and receives the voice data over your internet connection. For incoming calls, the process is reversed -- data packets arrive at your router and are converted back to voice audio in your handset.
What changes and what stays the same
| Feature | PSTN (old) | VoIP (new) |
|---|---|---|
| Phone number | Geographic 01/02 | Same number preserved |
| Phone handset | Plugs into wall socket | Plugs into router (or via adapter) |
| Dialling | Standard | Standard -- no change |
| Call quality | Standard voice | HD voice (typically better) |
| Works in power cut | Yes (copper carries power) | No (needs router + mains) |
| Works if broadband fails | Yes (independent network) | No (runs over broadband) |
| Emergency calls (999/112) | Yes | Yes |
| Features (voicemail, divert) | Varies by provider | Typically more features |
Call quality on VoIP
VoIP call quality on modern broadband connections is typically equal to or better than PSTN. Most UK providers support wideband (HD) audio which delivers clearer voice quality than standard PSTN narrowband audio. The main risk to VoIP call quality is a poor or unstable broadband connection -- if your broadband speeds are low or the connection is intermittent, call quality may suffer.
Ofcom requires VoIP providers to deliver call quality that meets minimum standards. If you experience significantly degraded call quality on a VoIP service, report it to your provider.
Emergency calls on VoIP
All UK VoIP providers are required by Ofcom to support access to the emergency services (999 and 112). Unlike traditional PSTN lines, VoIP calls may not automatically transmit your location to emergency services. Ofcom requires providers to give customers clear information about this before migration and to have systems in place to provide location data where technically possible.
Power cuts and VoIP
This is the most significant practical difference from PSTN. A traditional PSTN landline continued to work during mains power cuts because the copper telephone network carried its own low-voltage power from the exchange. A VoIP phone requires your broadband router to be powered, which needs mains electricity.
Ofcom requires providers to offer battery backup options to customers who identify as needing their landline during power outages -- particularly elderly customers, those with medical conditions, or customers in areas with poor mobile coverage. If this applies to you, request battery backup from your provider before your PSTN migration.
VoIP for businesses
Business VoIP services offer additional features beyond residential landline replacement: multiple lines on one number, hunt groups, IVR menus, call recording, softphones (VoIP on a computer or mobile app), and integration with CRM systems. Most business VoIP providers offer SIP trunking (connecting your business phone system to the internet) or hosted PBX services (the entire phone system runs in the cloud). Ofgem and FCA-regulated sectors should check that their VoIP provider meets any specific regulatory requirements for call recording and retention.
Related guides
Disclaimer: This guide is for informational purposes only. Kael Tripton Ltd is not regulated by the FCA and does not provide financial advice. Telecoms information is sourced from Ofcom, the UK communications regulator. Always verify current information at ofcom.org.uk.
Frequently asked questions
What is VoIP and how does it work?
VoIP (Voice over Internet Protocol) delivers telephone calls as digital data packets over a broadband connection. Your voice is digitised and sent over the internet to the recipient, where it is converted back to audio. The experience for the caller is identical to a traditional phone call, but the technology runs over broadband rather than copper telephone wires.
Do I need new equipment for VoIP?
Your provider will supply any necessary new equipment -- typically a new or updated router with a phone port, or a separate adaptor. Your existing telephone handset can usually be used with a VoIP service via an analogue telephone adapter (ATA). In some cases a new VoIP-compatible handset may be provided. Equipment is typically supplied at no extra cost as part of the PSTN migration.
Will my phone number change when I move to VoIP?
No. Your existing landline number is preserved when migrating from PSTN to VoIP. Ofcom's number porting rules ensure continuity of your geographic (01/02) landline number through the technology transition.
What happens to my VoIP phone in a power cut?
A VoIP phone requires your broadband router to be powered, which needs mains electricity. If the power goes out, your VoIP phone will not work unless you have a battery backup unit. Contact your provider if you need your phone to work during power cuts -- Ofcom requires providers to offer battery backup to customers with this need.
Is VoIP call quality as good as a traditional landline?
Typically yes, and often better. Most UK VoIP services support HD (wideband) voice which delivers clearer audio than standard PSTN. Call quality depends on the stability and speed of your broadband connection -- a poor broadband connection may result in degraded call quality.
Can I make emergency calls on a VoIP phone?
Yes. All UK VoIP providers are required by Ofcom to support access to 999 and 112. However, VoIP calls may not automatically transmit your location to emergency services in the same way as PSTN. Your provider must inform you about how location data is handled before migrating you to VoIP.
What about fax machines on VoIP?
Standard fax machines typically do not work reliably over VoIP because fax uses analogue tones that do not transmit well as voice data packets. If you need to send or receive faxes, consider an online fax service (which sends and receives faxes via email) as an alternative to a physical fax machine.
Does my telecare alarm work on VoIP?
Not necessarily. Many telecare devices (lifeline alarms, personal alarms) were designed for PSTN and may not work correctly over VoIP without reconfiguration or replacement. Contact your telecare device supplier before your PSTN migration to check compatibility and arrange any necessary changes.
