Abstract: A system and a method respectively for controlling telecommunications subscriber units via PC. The system comprises a number of PCs, a number of telecommunications subscriber units and at least one exchange arrangement including switching functionality. The exchange arrangement comprises a mobility server including third party control means. To the mobility server a number of PCs are connected vid a local area network. The PCs communicate with the mobility server via a third party control interface and each PC comprises an application for screen based telephony services. This application use a first party control interface for a user communication and each PC comprises converting means for converting between first party control interface operations and third party control operations so that the user can use first party control based applications together with third party control means in the mobility server.