Hi , I have a Siemens HICOM 350H PBX system with 500 lines . I want to buy another PBX system which is IP enabled and tie both of these in order to have a total of 1000 lines . One of the options is through ISDN line and the other through Fiber optic cable. what would be the hardware required on both the ends for the purpose. It would be nice if details for both configurations are provided. regards anik