Moving Over To SIP

BT have announced that as of 2025, ISDN lines will be terminated. This means that businesses across the UK will be moving over to SIP. This is not something to worry about, as T2K can help you throughout the transition.

Discover on this page everything you need to know about moving over to SIP (VoIP).


Reduce Costs

SIP Trunking can save on call costs and line rental changes, business continuity and calling and network features in comparison to traditional fixed line service.


Number Flexibility

Unable to take your number to your new office? With T2K SIP trunks, this isn’t a problem as you can use area codes from anywhere in the UK and point your non-geographic to your SIP Service.


Peace of mind

With T2K SIP we can provide automatic failover to your other sites, the ideal solution in the event of a disaster or unforeseen event such as an office power cut to keep your business running smoothly.

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Changing The Way You Communicate

Today’s business climate calls for reliability, agility and flexibility. In order to deliver on these core goals, the tools companies need to communicate to their customers and the wider world must be future ready and fit for purpose.


However, that is not always the case. Many companies are still relying on traditional Integrated Service Digital Network (ISDN) technology for their business communications, most of which are now becoming obsolete in a business environment where terms of interaction are dictated by increasingly demanding customers.

Flexibility Of SIP

Unlike ISDN, phone numbers are not tethered to a set location, giving SIP trunking the benefit of portability.


Businesses can automatically divert calls to a separate office location if all the lines at one office location are occupied (even if your offices are located in separate countries), and should your business choose to relocate, your current numbers move with you.


Having too many or too few channels is a familiar problem for most businesses with ISDN. With no limitations on DDI ranges and as many as 2,000 channels on a single connection, SIP eliminates this issue by enabling businesses to instantly scale, up or down, on a per channel basis to reflect their fluctuating needs.

3 Reasons Why Businesses Are Switching To SIP

Immediate Cost Savings With SIP

SIP trunking is not only less costly per channel for line rental than ISDN, but can also deliver savings on call costs. T2K can provide packages with free call minutes, saving you even more money.


SIP trunking requires less physical infrastructure, with fewer lines needed than with ISDN, in turn reducing the maintenance costs on required PBXs. This is all the more important for enterprise businesses, who are likely to have multiple offices and more lines.


SIP Allows Easy Business Growth

The beauty of a modern communications solution is that the addition of new lines and new office locations becomes a simple, pain free process. Line capacity to meet demand can be managed effectively without fuss and in most cases, call routing can be controlled easily, without requiring support from a supplier.

Importantly for growing businesses, it means that setting up new offices and remote workers does not require entire teams to stop working for installation to take place. Implementation can be seamless and in most cases the impact on productivity is minimal, if at all.


Number flexibility with SIP trunking ensures that if you are changing office completely, you can keep your existing numbers, even if you are moving to a different geographic location.

Outstanding Reliability With SIP

When a traditional ISDN connection goes down, it can be for days rather than hours. Also, businesses are reliant on their provider for a resolution, or to implement expensive call forwarding options reactively until the problem is resolved. A modern solution, like SIP trunking or a fully-hosted phone system, comes with in-built resilience features. These solutions ensure that if something goes awry, business continuity can be maintained, with instant failover of voice traffic on to a different line or call plans that can include immediate redirection of calls to different hunt groups, office locations or even mobiles.

Due to this, thousands of UK businesses have identified cloud-based telephony as the future-ready technology they need to enable growth and agility.



What Is ISDN?

ISDN is a communications network that relies heavily on physical infrastructure, specifically copper wiring. It came to prominence because it provided the opportunity to transmit voice and data over the same lines. However, because of its reliance on physical infrastructure to manage calls and additional functionality via a PBX (or multiple), this takes up space within business premises and requires resource to administer and maintain.

Similarly, it is hard to add and remove new lines to an ISDN network because it requires physical addition and removal.

What Do I Replace ISDN With?

The future-ready solution is SIP trunking. SIP is a ready-made replacement for ISDN, connecting a business’s PBX to the provider’s national network via broadband, Ethernet or a private circuit.

SIP emerged through a growing need for reliable, flexible and scalable communications technology that enables growing businesses to manage communications effectively in line with demand and is already prepared for voice and data convergence further down the line.

Will Our Telephones Go Down During The Switch?

SIP can work alongside ISDN, so the switch needn’t be fraught with the panic of turning one system off and another on at the same time. Costing will also be included within this part of the process.

During this period there should be little or no disturbance to your business. And any tests or checks can be carried out in a controlled environment.

Will We Need To Increase Our Bandwidth?

In most cases, yes. Many businesses however already have sufficient bandwidth in place to handle the extra strain of SIP. 

Don't see this as a negative. Extra bandwidth can be a huge asset to businesses who are struggling with slow internet speeds, looking for HD calls, or thinking of expanding in the near future.

T2K can provide you with many different types of internet solutions ready for this at the best price possible. 

Additional SIP Information

Unlike ISDN, a modern SIP-based phone system can integrate with business applications including Skype for Business. It also comes with built-in resilience and business continuity features. Each of these will be tested thoroughly before anything goes live to ensure the new system is working as expected.


If you're still looking for information regarding a potential move to SIP, call our head office directly on 0808 202 3200 for fast and professional advice. Alternatively, use the livechat box at the bottom right of your screen.

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Our Core Values

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    Your Business Makes Our Business

    We're passionate about what we do, and your business is our priority - without it we don't have one. That's why we only fit the most up-to-date equipment at the best price possible for you. All of this, paired with the best support we can provide. You could consider us geeks when it comes to telecoms systems.

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    Only The Most Qualified For The Task

    All of our engineers have the correct Mitel and Gamma Horizon accreditations to install and support your system. You should be safe in the knowledge that any support you receive will be the best at all times.

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    Two Ears, One Mouth

    We operate with the philosophy; two ears one mouth. Listening to your needs and requests first, then advising from our experience and expertise, taking into consideration your budget and requirements to provide you with the perfect telephone system for your business. 

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    The Full Package In One Place

    We take care of it all from start to finish, no matter what telephone system you require. We supply, Install and maintain all of our systems. Giving you that priceless peace of mind that there won't be too many cooks involved into the mix. 

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    A Genuine Value-For-Money Service

    Quality is key to a long lasting telephone system. Regular maintenance and well-sourced, up to date products, are at the forefront of our business. With that in mind, you can be rest assured that your spend becomes an investment into a properly working, long lasting system that will serve you for years to come.

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    We're Not Satisfied Until You Are

    We take pride in our work, carrying out installs as if they were our own property. If you’re not satisfied with any aspect of the work carried out, we're not either. We try, where possible, to make the system as unobtrusive to your office decor as possible; concealing cabling, holes or system components along the way.

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Contact Us

Here at T2K, we believe that there is no question too big or too small. Whatever your enquiry may be, from pre-sales, support and costs of products, we can help you every step of the way.


Please use our contact form to contact us. We aim to get back to you within 24h, although this will probably be quicker.


If you're a little bit form-shy, give us a call. Our friendly and helpful engineers or pre-sales team will do everything they can to make sure you get the help and support you need with every phone call you give us.


Call now on 0808 202 3200.