Abstract: In a communication system including a local area network (LAN), first and second LAN telephone gateways connected to the LAN, a speech network, first and second private branch exchanges (PBXs) connected to the speech network and to the first and second LAN telephone gateways, respectively, and first and second telephone sets connected to the first and second PBXs, respectively, a first speech path is realized from the first telephone set via the first PBX to the first LAN telephone gateway. Then, it is determined whether a second speech path from the first LAN telephone gateway via the LAN, the second LAN telephone network and the second PBX to the second telephone set is possible or impossible. Then, after the second speech path is determined to be possible, the second speech path is realized. After the second speech path is determined to be impossible, a third speech path is realized from the first LAN telephone gateway via the first PBX, the speech network and the second PBX to the second telephone set.