Some telephones, depending on the brand and model, have the intercom function, which allows to begin communication by sending the signal. When the signal comes, the telephone set rings a signal different from the standard ring tone call. After that the telephone temporarily switches off from the telephone line and works as an intercom.
Evolutiontel is an Australian owned company specialising in Voice over Internet Protocol (VOIP). Our first project was to provide a VOIP service that allows voice and video calls over the internet without sacrificing quality.