SIP is an acronym for Session Initiation Protocol. SIP works in conjunction with VoIP and is a communications signalling protocol that creates, modifies and terminates sessions with users. Essentially, SIP is used to start and end VoIP calls and is what establishes the session, so you can talk over the Internet.

A Private Branch Exchange (PBX) often takes the form of a physical cabinet or box that sits in an office and routes incoming and outgoing calls to different phone extensions. Consumers are now leapfrogging PBX systems in favor of space-saving hosted VoIP Providers, which route calls online via the Cloud.

ISDN first arrived in 1988 and is an abbreviation of Integrated Services Digital Network. Traditionally, this allows the transmission of speech and data over copper telephone wires. An aging and inflexible system, ISDN is being phased out around the world in favor of the scalability and ease-of-use of VoIP phone systems. BT (British Telecom) has announced that it will be phasing out all UK ISDN lines by 2025.

PSTN is a Public Switched Telephone Network and is a term used for the traditional landline. It uses circuit-switched telephony, with physical lines and automated telephone exchanges needed to make phone calls. Again, much like ISDN, this method of telephony requires engineers and installation and is seen as being less flexible than VoIP.

POTS excitingly refers to the term 'Plain Old Telephone Service' and is a term that is often used in place of PSTN.

Dual Tone Multi-Frequency signalling is a telecommunication signalling system which is generated when a telephone touch key is pressed. Each key generates two tones of specific frequencies. DTMF is also referred to as 'touch-tone'. The touch-tone keypad eventually replaced the rotary dial that was used early on in the evolution of the telephone.