I have a mod ics with 6.0 software it is configured with 2 T1 one is connected to PSTN with DID # I have their main # going to a target line 200 and that is set to ring on station 1000 and 1001. when a call comes in it rings at both stations but once ex 1000 answers a call, the next caller rings at ex 1000 but not ex 1001. how can it ring on both phones all of the time so they can answer it?