Business Phone Lines - Your Definitive Guide In 2024

Finding a business phone line provider in the UK in 2024 can seem like a daunting prospect. Not only are there a plethora of providers to choose from, but there’s also a significant amount of technologies involved, each with its acronyms and jargon! In this guide, we look to demystify the world of communications, enabling you to find the best phone line and service for your business. If you’d prefer to speak than reading, please request a quote or use our live chat, and one of our telecoms experts will be more than happy to help.

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Many of you will have landed here looking to find out who are the best business phone line providers, so here is a quick rundown of who we believe are currently out in front in a league of their own:

  1. T2k
  2. Gamma
  3. Kcom
  4. 4Com
  5. Lily Comms
  6. Reach Digital
  7. Spitfire
  8. Ring Central
  9. XLN
  10. Vodafone
  11. BT
  12. Plusnet
  13. Virgin Media
  14. Zen
  15. O2
  16. Toople
  17. Woav

Business landline contracts

All business landline contracts, be that ISDN, PSTN or VoIP, will incentivise you to sign up for a longer-term agreement. It’s often in everyone’s best interest to have a longer deal as it means that all parties have the continuity of knowing the service will be in place for that period. 

You can, of course, choose to have a shorter contract, as a reasonable number of our customers do, but what you gain in flexibility, you lose in discounts and service continuity.

What is right for you and your business will, of course, be unique, so when you speak with your T2k account manager, be sure to raise the topic of contract length so you can discuss what is best for you.

Business phone lines
Business phone line providers come in all shapes and sizes

Glossary of business telecoms terms

Business telecoms is a field dominated by acronyms and jargon, so we’ve created this next section to help you navigate our world as best as possible. Remember, if you have any questions and want to speak to a telecoms expert, please get in touch via phone or using the live chat feature of our website.

What are business phone lines?

A business phone line is simply a landline used by a company rather than a domestic property. There are several different business lines to choose from, but with traditional PSTN and ISDN technologies being phased out by BT, most businesses are now switching to VoIP. 

If you want to know more about the latest technology, be sure to check out another of our recent guides titled “What is VoIP?” where we explain everything you need to know about it.

PSTN landlines

PSTN landline is what many people in the UK will think of when you say “phone line”. The public switch phone network to give it its full name was introduced in the 1800s and has been the foundation of UK communications ever since. Businesses have used PSTN services as their primary method of transmitting telephone calls and faxes for many years, with the network being re-purposed in recent times and used for internet access. 

Millions of people and indeed businesses continue to use and rely on the UK’s PSTN some 140 years after it was first introduced, so the fact it is being turned off soon is nothing short of historic. As we will get into later in this guide, all businesses and consumers will need to move to another type of phone service before the big switch off; most expected to use VoIP via a cloud-based phone system such as our Horizon platform.

ISDN Landlines

ISDN or integrated services digital network is a business telephone service that allows for the simultaneous transmission of voice, data and video on the digitalised circuits of the PSTN. First introduced to the UK on June 25th 1985, it was initially called Integrated Digital Access (IDA). It was used to extend the digital phone network to customer premises, allowing for faster data transmission than traditional analogue lines. In the mid to late ’90s, ISDN (ISDN2) was used by schools, businesses and other organisations to achieve faster internet speeds. At the time, most analogue dial-up connections would give you between 28kbits/sec to 33.6kbits/sec, whereas a single ISDN channel was up to twice as fast. Another significant benefit of ISDN over analogue lines for internet access was that a connection could be made quietly and in just 1 second. Compare that to dial-up modems, which would be screaming at you for 10-15 seconds; it was an altogether more pleasant experience.

Over time and as technologies developed and ADSL was rolled out, businesses looked to use ISDN primarily for phone services, as it allowed for many more concurrent calls over a single line.

ISDN Business phone lines
ISDN and PSTN networks will be switched off in 2025

ISDN2 and ISDN2e

ISDN2 is the lower capacity version of ISDN, which is capable of handling two phone calls simultaneously. Often the best choice for small businesses, it can also be upgraded to support 60 concurrent calls. One of the most significant benefits of ISDN and ISDN2 is that you can use a range of numbers (DDIs) to have multiple phone numbers connected to the same physical line.

Benefits of ISDN2

  • Capacity - ISDN2 lines can handle two calls at the same time.
  • Scalability - ISDN2 can be expanded to support up to 60 channels.
  • DDIs - ISDN lines support number ranges, so you and your team can have your phone number (DDI).

While there are undoubtedly significant benefits of ISDN for businesses, it’s not without its disadvantages.

Disadvantages of ISDN2

  • Expensive to install - ISDN lines are complex and often costly to install, costing several hundred pounds. Not only that, installation typically takes several weeks. 
  • Line costs - ISDN is charged on a per-channel, and with each costing a similar amount to a PSTN line, the costs can quickly add up.
  • Equipment costs - ISDN lines require a PBX or router with a BRI card installed to work, which means you can’t simply plug handsets into the service.
  • Maintenance of equipment - Once you invest in a business phone system, you’ll want to make sure that it’s well looked after, so you’ll need a service contract with a telecoms company such as ourselves. 

Despite the higher costs, ISDN and ISDN2e are still widely used by many businesses, although many are now switching to VoIP

Joining T2K is one of the best if not the best business decisions we've made.
Paul Crisell - Vale Veterinary Clinic
on Google


ISDN30 is the next step up from ISDN2, with the most notable difference being the number of channels you can scale up to. ISDN2 tops out at 60 channels, ISDN30 supports eight at the lower end, with each line capable of having 30 voice channels. I know 30 is half of 60, so how is ISDN30 capable of more? Unlike ISDN2, ISDN30 lines can be bonded so that you can have multiple ISDN30 lines going into the same phone system. Not only can ISDN be used for phone calls, but the data capacity allows for very high-quality video calls and even site to site communications. It’s perhaps easy to see why ISDN30 has been the connection of choice for larger businesses for some 20 years. 

Benefits of ISDN 30

  • Hugely scalable - bond lines together to scale your channel capacity.
  • High data transfer rates - use ISDN to host high-quality video conferencing and transfer large amounts of data.
  • Reliability - ISDN30 business services are robust and typically come with very high SLAs, meaning should you get any issues, they’ll generally be resolved promptly.

VoIP phone service

A VoIP phone service allows you to make and receive calls over the internet, rather than the old PSTN and ISDN networks. There are a few ways you can start using VoIP, which is best for your business will depend on your requirements.  

How VoIP phone lines work
With VoIP your phone calls are transmitted over the internet

How can my business get VoIP?

  1. Your existing phone system may already be VoIP compatible, or it might be possible to install new components to upgrade it to VoIP. In some cases, your current office handsets can even be used, removing the need to replace everything, so it pays to speak to a telecoms company, such as ourselves, before making any decisions. At T2k, we have nearly 30-years of experience installing and supporting business telephone systems and today; we work with a wide variety of technologies, including VoIP. 
  2. For businesses with a significant number of people at a single site, and even those spread across multiple locations, it can be more cost-effective to buy a VoIP phone system than subscribing to a hosted service such as that mentioned in option three. One thing to bear in mind with both using an existing system or installing a new one, you’ll need several SIP trunks from your VoIP provider, which will enable you to make calls over the internet. 
  3. The final option is to subscribe to a hosted VoIP system, like our own Horizon platform. A cloud VoIP system is provided to you as a service rather than buying and owning any equipment. This gives you access to many features, excellent reliability and room to grow, all for a predictable ongoing subscription fee. Businesses of all sizes can benefit from a hosted VoIP service. With many employers and employees moving towards flexible working, having your phone system located in the cloud rather than your office gives you the adaptability you need.

Benefits of VoIP

Far from being merely a replacement for PSTN and ISDN services when BT turns those off in 2025, VoIP, like many other internet-based technologies, brings a diverse set of benefits to businesses, including:

  • Reduced call costs - significant savings on both domestic and international calls
  • Advanced features - such as call recording, auto attendant and time of day routing
  • Better CRM integration - works with your favourite tools, moving you towards Unified Communications.
  • Excellent handsets and headsets
  • Softphones that allow you to turn your computer into a handset
  • Better call quality - HD calls and crystal clear quality.
  • Future proof - the latest technology
  • Scalable - scale your service up and down as required
  • Flexible - work from anywhere as long as you have an internet connection.

Why businesses are turning to T2k

With many companies to choose from for your telecoms, it can be somewhat challenging to determine which is best for your business. While we are, of course, biased, we think that for many companies, you’d be hard pushed to find a company better suited than us. Here’s why

The VoIP phone system from T2k has saved us serious expenditure and has changed the way we work for the better.
Steve Knell -Altogether Care
on Google

About us and our services

T2k has been providing telephony services, including business phone lines, for nearly 30 years. We’ve built up a loyal customer base of companies that value excellence in customer service and want on-demand tech advice tailored to their business during that time. Many of our customers have been for over a decade, with a good number with us for much longer than that. We should point out that we’re not a substantial international business; we’re a small team of telecoms experts that work together to provide a service that is hard to beat. From our offices in Dorset, our sales, customer service, and technical teams look after a broad range of setups, from traditional and onsite VoIP phone systems through to cloud-hosted VoIP and connectivity, 

Why T2k:

  • Nearly 30 years of experience working with businesses like yours.
  • Not a big faceless organisation, we’re real people who would be more than happy to meet you for a coffee.
  • Continuity of staff, many of our team, have been with us for over 20 years, so you will always be speaking to someone who knows about your business systems.
  • Competitive pricing owing to long-standing relationships with all of the significant providers.
  • A one-stop-shop, we can provide everything from your handsets and softphones through to your phone system and VoIP numbers
Lee Clarke
Sales Director

Having worked for T2k for nearly 25 years, it's fair to say that Lee is an expert when it comes to all things telephony and business communications. Overseeing the commercial side of the business, he has helped the company evolve and grow through the decades. In recent years, and with the advent of VoIP and hosted telephony, Lee has made sure that T2k is at the forefront of technological developments. With a firm interest in helping businesses navigate the world of telecoms, Lee is responsible for the majority of the content on this website.

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