There are 2 types of PBX - one uses the analog line while the other uses the digital line. The Private Branch Exchange (PBX) mentioned here refers to the digital line type.
As the built-in modem of the VAIO computer is a device designed for use with the analog line, connecting it to the digital line may cause failure, resulting in heat or fire to the modem. In addition, some PBX's for the analog line may not meet the specifications for the modem to work. Therefore, before connecting to the PBX line , please check the specifications of the PBX with the maunfacturer.
The following information can be located in the online manual and user guide:
The internal fax modem can be connected to the subscriber telephone line. Do not connect it to the PBX (Private Branch Exchange). Connecting to the PBX may cause a failure or fire. Never connect it to the line for home telephones and business phones in particular.