Voice over IP, VoIP

Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet telephony, broadband telephony, and broadband phone service specifically refer to the provisioning of communications services (voice, fax, SMS, voice-messaging) over the Internet, rather than via the public switched telephone network (PSTN), also known as plain old telephone service (POTS).

Wikipedia

The main difference between IP telephony and traditional telephony is packet switching, not circuit switching. In traditional telephony, from the moment of a call to the end of a conversation, several operators at once allocate a separate communication channel, unlike IP telephony, where packet switching is used, and the channels themselves can be used in multi-user mode.

This allows reducing the cost of a call due to more efficient use of operators’ channels, as well as flexibility in the implementation of call routing. So this allows you to improve the quality of communication to support HD, video calls, support for multi-user conferences and a large number of additional services implemented using PBX. To take full advantage of IP telephony, you need a cloud PBX service, or connect your PBX using a SIP-trunk service.