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Phone lines geared for larger businesses.


Appear more professional and improve your business' phone lines by switching to ISDN. It's easy!

Originally analogue phone lines were the only option for the entire telephone network; this meant that there were no complications for a small business having to choose the most beneficial type of phone line for their company. As technology has developed, different options for phone lines have arisen and all of them offer different features to support your business. ISDN (the Integrated Services Digital Network) phone lines are a much more professional choice of telephone line, in comparison with basic analogue lines.

Switching your analogue phone line over to ISDN phone lines with DuoCall is a simple and hassle-free task that gives you access to competitive rates with the highest level of customer support in the industry! Designed by our business for your business.

DuoCall's ISDN phone lines - Sheffield

So what are ISDN phone lines?

ISDN phone lines combine the benefits of analogue and digital data together over the same network. This means that data in the form of voice, images, text, and video can all be carried over the same network.

ISDN phone lines also provide a single interface for all of your communication devices including your phone, your video-phone, your fax machine and your computer etc.

DuoCall's ISDN phone lines - Sheffield

What options are available when switching to ISDN?


ISDN2 (ISDN2e if we’re being pedantic!) is the preferred telephone line for businesses that require between two and eight voice connections in the UK. 

Each ISDN2 circuit provides two speech channels, so if your business needs four simultaneous speech paths, you need two ISDN lines (circuits). If you require six simultaneous speech paths, then you will need three ISDN lines etc.


If you’re a larger business and you need between eight and thirty voice connections simultaneously, then ISDN30 is the best option for your company.

ISDN30 is supplied on a circuit bearer which offers a minimum of 8 channels (voice lines) and a maximum of 30 channels. If your business needs more than 30 voice lines then you would require two ISDN30 circuit bearers.

DuoCall's ISDN phone lines - Sheffield

What are the benefits of switching to ISDN?

1. DDI numbers

1. DDI numbers

2. Call diversion

2. Call diversion

3. Switching is easy

3. Switching is easy

1. DDI (Direct Dial Inward) numbers

DDI numbers allow your business to associate additional numbers with your main number for your ISDN circuit. This means that each telephone extension can have an individual number; your business will be able to allocate numbers for different handset users and for different groups or departments etc. You can even allocate DDI numbers for marketing purposes and use one of our Inbound Numbers to highlight the number.

DuoCall’s DDI numbers are available in groups of ten.

DuoCall's ISDN phone lines - Sheffield

2. Call diversion

Connecting your ISDN2 phone lines to your phone system will allow you to divert calls to external numbers seamlessly.  When a call comes into the office on channel one, it can then rerouted out of the office to an external number on channel two; it couldn’t be easier!

Call diversions will enable you to stay connected to your external staff with ease as well as giving your business the opportunity to reroute incoming calls externally when the office is empty.

DuoCall's ISDN phone lines - Sheffield

3. Switching to ISDN phone lines is easy!

Switching phone lines can be very daunting for a business. Small companies can’t afford to take the risk of experiencing hold-ups during the process of changing from one phone line to another. It’s economically unsustainable for them to turn off their phones for a long period of time whilst their line is being changed, but when switching to ISDN there’s really no need to worry.

ISDN can run over the existing copper cables used for your analogue phone lines. Don’t worry about an expensive charge for switching to ISDN, the process is fast, simple and is an economically-favourable option for your company!

DuoCall's ISDN phone lines - Sheffield

4. Get HD voice calls and multi-task!

Switching to ISDN phone lines will sharpen the quality of your voice calls.

Are you tired of crackling? Well ISDN2 and ISDN30 offer your business high definition telephone calls. We all know that a high quality phone call provides a high quality service for your business!

Multiple phone lines enable you to ‘multi-task’. Use one telephone line for your calls whilst you use another ISDN line for transferring your company data.

DuoCall's ISDN phone lines - Sheffield

5. Combine lines for a higher bandwidth

Add more and more ISDN phone lines to improve your bandwidth further. Don’t transfer your data slowly; make sure your files are transferred quickly and efficiently. Change to ISDN phone lines today and improve your upload and download speeds straight away.

What Can I Do Next…

  • Call our friendly Sales Team with any queries or feedback on 0333 313 5000
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  • Find out what our customers say about us in our Case Studies section

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