Does the SEM-DSC PowerSeries support phone line communication (POTS)?

No. The System Enhancement Module (SEM) for the DSC PowerSeries must always be the primary communicator and cannot be used in conjunction with a phone line communicator (POTS). 

Phone line backup is not a certified configuration with the SEM - DSC PowerSeries and is not supported.

If a phone line was used previously or the panel is brand new, it is important to disable any settings related to Phone Line (POTS) communication. For more information about clearing phone line settings, see Clear a Phone Line Failure on a SEM-DSC PowerSeries.