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Jargon Buster - Voice, Communications and IP Telephony

The withdrawal of PSTN services by BT in 2025 means consumers need to look at their VoIP (Voice-over-Internet-Protocol) options if they want to avoid disruption to their communication services. 


Switching to VoIP presents many opportunities but a significant amount number of organisations and residential customers are still unaware that the switch-off is even happening!

For those that are aware, technical terms, confusing acronyms and IT jargon can cause confusion and make it hard to decide which option is best for you. 

With this in mind, we’ve put together this handy guide to some of the most common VoIP related technical terms that you need to know.


Analogue Telephone Adapter (ATA)

This is a small box that adapts an analogue phone for use with a digital VoIP telephony system - it might also be used to connect modems into VoIP systems and/or adapt fax machines.

Auto Attendant

This may also be known as a Virtual Receptionist. It allows callers to be transferred to an extension without first needing to speak to an operator or receptionist.

Business Continuity

In this context, a term used to describe the way in which an organisation can continue to operate digitally and maintain essential functions during and after a disaster.


Also known as ‘click-to-talk’, ‘click-to-chat’ or ‘webcall’. This is a form of web-based communication that allows a person to click an object (for example: a ‘call now’ button on a website) and for a number to be immediately dialled.

Cloud Telephony

This is another term commonly used for VoIP. It most often describes ‘hosted’ VoIP which uses Cloud-based IP networks rather than requiring users to have hardware on-premises to make calls over the internet.

Customer Premises Equipment (CPE)

This is on-premises IT hardware that, in this context, enables voice communications.

Computer Telephony Integration (CTI)

Also called ‘computer-telephone integration’ is a term used to describe any technology which allows telephone and computer communications to be integrated.

Digital Enhanced Cordless Telecommunications (DECT)

A protocol used to provide wireless telephones so they can be carried around and plugged into a base for charging.

Direct Routing

This allows users to make and receive calls from Microsoft Teams. It describes the process by which this is enabled and that allows calls to the PSTN (i.e. the traditional telephone system).

Direct Dial Interface / Direct Inbound Dialling (DDI/DID)

Known as DDI in the UK and DID in the US, both terms describe the same function. Essentially a DDI/DID is your telephone number which with VoIP is often a 0330 number or geographic.


When speaking about VoIP, this normally refers to hardware including analogue, IP or conference phones, as well as softphones or UC clients.

Fixed Mobile Convergence (FMC)

FMC refers to services that allow subscribers to switch between fixed wired and wireless/mobile networks seamlessly.

Hosted VoIP

Hosted VoIP (or cloud hosted VoIP) means your telephone systems are hosted and maintained by your telephony provider in the Cloud. You don’t need on-site equipment other than handsets - which themselves are optional if you use Softclients (see our definition of softclient below).  

Hosted Telephony

See our Hosted VoIP definition above.

Hosted Voice

See our Hosted VoIP definition above.

Hunt Groups

A method of distributing calls to a single number (e.g. your organisation’s main telephone number) to a group of pre-defined extension numbers. Typically, there are four choices for how calls should be distributed amongst the group: simultaneous, regular, uniform, and circular.

Instant Messaging (IM)

This is a type of online chat which transmits messages over the internet in real-time.

Internet Protocol (IP)

These are the rules which govern and the methods by which data is sent over the internet from one computer to another.

Internet Protocol Address (IP Address)

An identifier given to each device connected to a network. You can think of it a bit like your postage address in that it helps data find its way to/from your device over the internet.

IP Communications

In this context, it is normally used in reference to Voice-over-IP (VoIP) and SIP communications.

IP Phone

This is a telephone that plugs into your network as opposed to a telephone line. It uses IP (see our definition above) to receive and transmit calls.

IP Telephony

See our definition for IP Communications. 

IP Voice

See our definition for IP Communications.

Integrated Services Digital Network (ISDN)

An ISDN connection handles multiple calls concurrently and links to a PBX/PABX. Unlike a SIP trunk which uses IP to deliver voice and data, ISDN uses traditional copper PSTN.


This is the time it takes for something to occur; in this case it means the time taken for a call to be transmitted to an endpoint (e.g. from one VoIP phone to another). Latency is measured in milliseconds and too much of it can cause poor call quality.

On-Premises VoIP

Your VoIP system hardware is installed at your organisation’s premises, as opposed to be hosted and maintained in the Cloud by your VoIP provider.

(Data) Packets

Packets carry data transmitted over the internet in the protocols (see Internet Protocol) the internet uses. VoIP changes analogue voice signals into data packets which are then sent over the internet.

Packet Loss

Data Packets (see above) can be lost whilst they are being transmitted. This can result in poor call quality.

Plain Old Telephone Service (POTS)

POTS simply refers to a traditional, standard analogue telephone line.

Private Branch Exchange (PBX)

A PBX is a private telephone system within an organisation that switches calls between users on local lines. This allows multiple users within an organisation to share a number of external phone lines. Traditionally, these systems have human operators who receive external calls and direct them to internal users.

Private Automatic Branch Exchange (PABX)

A PABX is similar to a PBX (see our definition of a PBX above). The primary difference is that a PABX is automatic and doesn’t require a human operator to direct calls. Both terms, however, are often used interchangeably.

Public Switched Telephone Network (PSTN)

This is the traditional telephone network which uses underground copper wires. It is being switched-off by BT in 2025 which is why many organisations are considering switching to VoIP.

Session Initiation Protocol (SIP)

SIP is a common internet signalling protocol which is used for initiating, maintaining and terminating video, voice and messaging applications. For VoIP services, SIP turns voice into data packets (see our definition for Data Packets above) which can then be transmitted over the internet.

SIP Channels

This refers to the number of calls your organisation can make or receive simultaneously. If you’re a large organisation with a high call volume, you will likely need more SIP channels than a smaller organisation which makes few calls.

SIP Trunking

A SIP trunk is a technology that creates an internet-based link between your PBX/PABX and the traditional telephone network (PSTN). This allows users to make and receive IP calls without replacing their on-site PBX. A SIP trunk is made up of SIP channels (see our definition for this above).


A softclient (aka soft phone) is an app that allows you to make or receive VoIP calls from a smartphone, computer or a tablet. This means that users of VoIP services, such as YorVoIP©, don’t need to buy a new handset and can take their service with them wherever they are.


Used interchangeably with Softclient (see our definition above).

The Cloud

This term refers to the global network of data centres and remote servers which users can access over the internet.

Unified Communications (UC)

Unified Communications refers to an interconnected communications system that joins together different communication methods within an organisation, including VoIP, email, SMS, fax and IM.

Voicemail to Email

This feature allows voicemail messages to be forwarded to a specific email inbox.

Voice over IP / Voice over Internet Protocol (VoIP)

VoIP, also referred to as internet telephony, IP telephony or internet calling, allows users to make low cost calls over the internet. VoIP works by converting analogue voice signals into a digital format to be sent over the internet.

Wholesale Line Rental (WLR)

WLR is a product which allows telecommunication providers to rent access lines at a wholesale price from BT. Providers then resell these lines as their own product to end-customers - normally in the format of a single telephone line for calls only or packaged with broadband.



If you want to find out more about our YorVoIP services or contact us to discuss your requirements - contact us here!



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