An ISDN box, also known as a network termination unit, is a device that allows you to use two digital channels at the same time. It is used in systems with an ISDN digital line.
The device allows you, for example, to make two calls simultaneously or to use an analogue modem (or ISDN) while a phone is busy or while browsing the Internet.
This technology has now been overtaken by VoIP, which totally eliminates the limit on simultaneous calls typical of ISDN units.
Find out about this and the other advantages of the cloud PBX here.