Each 3300 in the cluster will already have a Cluster Element ID (CEID) that you can dial to get features across cluster members. You will also have a Feature Access Code (FAC) programmed for paging.
So for example your speed dial might be 4000 which points to 5001**91 - with 5001 being the CEID, **9 being the FAC for loud speaker paging on that system, and 1 is the group number.