ISDN30 has been the most popular way to connect a phone system to the public telephone network for organisations requiring more than 6 phone lines since around 1992.

If you want to know about ISDN30, then this web site is just what you need as it will give you all the information to enable you to make an informed decision. 


The first thing and most important thing you should know is that ISDN is old technology and is being phased out.

From 2020 you will not be able to order it and in 2025 it will be retired completely.

The alternatives to ISDN are VoIP based solutions all of which use the internet. So you need decent internet connectivity to use VoIP.

If you don’t have reasonable internet connectivity, ISDN may still be your only viable option for connecting your office to the public telephone network.

ISDN30 is now VERY UNLIKELY to be the right connection for you – call us for advice. 

You should really be thinking about upgrading ISDN30 to VoIP


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What are the alternatives ?

You simply have 2 choices….either SIP or a fully hosted system.

SIP is a direct replacement for ISDN and does exactly what ISDN does (and quite a lot more). You connect a SIP trunk to your phone system which allows users to make and receive calls via the public phone network. It is essentially an ISDN clone but works across an internet connection, rather than a direct BT Openreach-based digital switched circuit. So you still have a phone system control unit on your premises.

A fully hosted system is, again, internet based. But you don’t have a control unit as the phone system is ‘in the cloud’.

Which is better – SIP or Hosted? 

Good question….the answer is it depends. For small organisations of, say, less than 100 users, a hosted system is more likely to be better for you and for bigger organisations, SIP is probably more appropriate. But it does depend!

Your best option is to call us so we can understand your situation and give you some advice – 01892 578666.

We have been advising organisations on telecoms since 1994.


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Pricing and Costs

If you need ISDN pricing on ISDN30 installation and rental, please contact us using the contact button and we will respond immediately.

 We will provide the best pricing in the UK. 

For information on the different types of telephone systems available that can connect to ISDN30 please contact us on 01892 578666 or use the contact form.

Overview and Explanation 

If your business needs at least 8 simultaneous voice connections to the outside world then, that is what ISDN30 does.

ISDN30 can be installed by BT or any reseller of network services. You HAVE TO PAY FOR 8 LINES. Therefore, if you need, say, 4 lines, you should install ISDN2e. Please click here for details on ISDN2e. Note the functionality of ISDN30 and ISDN2e is identical. ISDN30 and ISDN2e only differ in their pricing (slightly) and the way in which they are delivered to your premises. 

How is IT delivered? 

ISDN30 is properly surveyed and pre-installed and the telephone system installation company can phone the carrier when they are ready to bring the lines into service so it can be installed with a degree of control. ISDN30 is delivered on copper wire or fibre optic cable. Note there are distance limitations with ISDN30 so premises in rural areas may really struggle to get it installed. The carrier can always install it but if it means that it has to be delivered over fibre cable  due to distance then this could cost extra – sometimes thousands or tens of thousands of pounds. Where ISDN30 is not available you will be forced to install ISDN2e which effectively gives you the same functionality, albeit delivered differently. 

ISDN2e delivery 

ISDN2e on the other hand is not surveyed. The appointment is booked and the BT engineers (yes BT engineers will attend regardless of who you are buying the lines from) will turn up and, more often than not, get the ISDN2e installed successfully. 

What number options area available? 

For most businesses, all you need is ISDN30 plus Caller ID and level 3 cover (Level 4 cover is now available which provides a 6 hour fix). You will also need an inbound number. Note all ISDN has limitations on the number of numbers. There are 5 number slots available. A slot can be taken by a single number or a range of numbers. A range of numbers has a minimum of 10 numbers in it in multiples of 10. 

Most businesses may have one single number (one slot taken) and a range of Direct Dial numbers (10 for a small company, 100 for a larger company and so on). This example would leave 3 slots free for future use for a single number or range in each slot. 

SIP Trunks or ISDN? 

Please note that SIP may also be a very good option for you.

Indeed, at the time of writing (2019), you would be mad to install ISDN30.

You should be replacing your ISDN connections with either SIP or go for a fully hosted phone system and ditch your premises based phone system (control unit/pbx). 

SIP trunks have replaced  ISDN and do have some advantages  – for example with SIP you can keep your land line number even if you are moving out of the BT exchange area (you cannot do this with ISDN). To find out more about SIP Trunking and the advantages of SIP, please click on the links here. 

SIP costs and SIP prices can also be found on this link – SIP Trunk

The main factor to consider with SIP is the connectivity. SIP is delivered on an internet connection. Therefore, the speed and reliability of the internet connection IS CRITICAL. The other critical issue is the equipment you are connecting it to. The manufacturer of the equipment MUST HAVE laboratory tested their equipment with your chosen SIP trunk provider. This is ESSENTIAL. 

If there is any chance that the internet connection is less than good, it may be better to stick to a traditional ISDN connection or upgrade your internet connection – we can tell you what type of connection you can obtain within about 5 minutes. 

Call us for advice. 

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