i have UCM6102 with 2 PSTN lines connected to 2 FXO ports. we want all incoming calls to use 1 PSTN line, such that when that line is busy on call, the next call is routed to through the Second but idle PSTN line.
That is a function of the telephone service provider. They manage how the calls are sent to the UCM. It is a service referred to as hunt or busy, call rollover and other names.
You should make sure that the service provider is also able to mask the outbound CID so that regardless of which line is used to make an outbound call, the callerID for both is the same and that of the number you want the public to see. If not, the provider will send the number associated to the line which then allows some to know the second line whereupon they may use it which defeats your purpose.
Thanks , this was useful