A telephone communication system and a method for IP-PBXs is disclosed. The system includes a cloud server, a plurality of IP-PBXs each provided with first voice call devices, and a plurality of second voice call devices. The IP-PBXs are registered in the cloud server, each IP-PBX is installed with a first application program, each first voice call device is assigned with a set of extension codes, and each IP-PBX uses the first application program to manage the voice call functions of the first voice call devices. The second voice call devices are registered in the cloud server, each second voice call device is installed with a second application program to perform voice call functions, and the cloud server assigns a set of system assigning codes to each of the IP-PBXs and the second voice call devices.