voip gateways provide an interface between traditional telephone interfaces such as PSTN Analogue, Basic Rate ISDN (ISDN2) and Primary rate ISDN (ISDN30) and the IP Network to enable telephone calls to be made over the IP network. The IP network could be as simple as connecting telephone systems at two locations over an existing leased line or VPN or could be used to connect homeworkers into the office PBX over broadband internet access.

The choice of a VOIP Gateway will depend upon the interfaces available on the telephone system eg. Analogue trunks, ISDN2e Trunks or ISDN30 trunks and the number of simultaneous calls required over the IP Network.