Datera Call-eX is a modern telecommunications server (IP PBX) for both large and small companies, which allows easy integration of previously introduced technologies into one coherent telecommunications system. System allows a transparent combination of all telecommunications technologies (e.g. traditional, ISDN - BRA/PRA, internet VoIP, mobile GSM) with devices comprising company's internal telecommunications intrastructure. As this integration is indroduced, all previously made investments in telecommunications infrastrucure of a company are fully retained. Datera Call-eX can also be successfully used for building a new telecommunications infrastructure.