Skip to content

The big switch off - VoIP and SIP – What’s the difference?

Since around 2008, where ever possible, transmitting voice services over an Internet connection* (rather than an analogue / PSTN or digital / ISDN phone line) has been in testing within the industry with clients and customers who were asked to be early adopters of this technology.  

There have been rumblings within the industry since 2008, that Openreach, the division of British Telecom PLC (BT), who own and operate the almost the entire UK Public Switched Telephone Network (PSTN), which also incorporates the Integrated Services Digital Network (ISDN2e and ISDN30e) will be switching off ALL of these services in December 2025.

Formal announcements of this ‘fork-lift’ change were finally announced to us in the industry in 2018 of the new products and processes that Openreach had been trialling in their network to be able to withdraw PSTN/ISDN services and thus, a bit like ‘Making Tax Digital’, all equipment connected to a pure ‘Copper’ network and is reliant on a ‘Dial Tone’ will, in effect, stop working.

*Voice over Internet Protocol (VoIP) and Session Initiation Protocol (SIP) is the replacement technology behind the ability of making a simple phone call from desk or DECT (cordless) handset. Both are based on Internet Protocol (IP).

But what is the difference between VoIP and SIP?

I was asked this question by a client as he had had a sales call suggesting to him that he was still on a copper phone line, when in fact he has been using a VoIP for several years and has recently migrated his service to my company.

The sales person insisted that SIP is the latest protocol and that he quote for a new system.

VoIP and SIP are the same technology in essence. A VoIP system is more commonly known as a HOSTED system, i.e. there are IP handsets on site, which connect directly to a ‘cloud’ based server where all the clever bits happen. Each IP handset attracts a monthly licencing fee and each person on line has the facility to make and receive a call. The licence fee includes all the features that one would expect from any traditional phone system. Voicemail, call transfer, call hold, call diversion, call recording, call records and so on.

SIP, put simply, are virtual phone lines that connect to a Hardware based system. E.G. An on-site system such as a Mitel, which is using ISDN2e/30e for calls, can be converted to accept a SIP Trunk, with multiple SIP channels (using an Internet Connection to make and receive calls, rather than the traditional BT exchange / PSTN service). The change means that the system will be part of the internal Local Area Network (LAN) and the ISDN card being made redundant making way for SIP channel licences. The principles and pricing are the same as ISDN2e/30e. If you had an ISDN30e and subscribing to 8 channels (max 30 channels / calls), in this example, 8 SIP licences would need to be paid for and activated in the Mitel System and you pay for 8 SIP channels (incoming / outgoing calls). There is NO other system change!

Seeking Good Advice

Now is the time to review what types of phone lines and broadband services you have in your business as there are so many variations and factors to take into consideration.

There is not long to go now until December 2025 and there is no guarantee that Openreach will delay any PSTN switch-off for the reasons mentioned above about phone lines that special types applications other than making a phone call.

We recommend that you seek specialist advice if you are using any standard phone lines and especially if you have a telephone system such as Avaya, Mitel, Alcatel-Lucent, Nortel, Panasonic, Samsung, Siemens HiPath, Shortel, Toshiba to name but a few.

There are around 50 (more or less) VoIP / SIP products and services on the market so the key element to choosing a new system is asking yourself, “does our current system fulfil our business practices?”

If the answer is yes, then look for those features first and then add the extras that modern VoIP / SIP functionality can bring to enhance those business processes.

Until next time –

Pritesh Ganatra FITP

Pritesh started his career in 1990 in the Consumer Electronics industry, initially selling consumer ... Read More