we have 3 PRIs, al connect to the same gateway(3825). We need to set up the next incoming or outgoing call will go the 2nd PRI if the first one is full. Should we configure that in CallManager, if so, how to do that? or we just need to call the Telco to set it up?

To make the 1st PRI full, someone in the forum said use the 1st phone to 2nd phone, hold it, and use the 2nd phone to cal the first one, etc, but how can I achieve that if every phone only has two line assigned?

Thanks