This module extends the system to two ISDN ports - with voice-over-IP phones, it has nothing to do. You can see the two ISDN ports use internally or externally (individually selectable), internally then you have the choice between S0 (for several phones, the two voice channels per port sharing) or UP0 (only one telephone per port). The module works properly with us for 2 months in UP0 mode. The installation is really simple - plug and wire - the choice of Port-mode bugs me a little, because this is necessary to implement a huge jumper that "stuck" in many PINs. If necessary, are a pair of tweezers and tact beneficial. A DIP switch would in my view better ... Or a change in software in the web interface of the system.
