It is a method of communication based on text messaging between two fax machines, the first one calling to other one to send a fax, the recipient receives a text on A4 paper and after that communication process ends.
AddPac AP-GS1004A is one of the models of inter-network VoIP GSM gateways, through which, it is possible to format a single network unit and to use it for VoIP-telephony, analog communication lines and GSM-network.