I have a customer with a 450 and 3 50's. All 4 of these systems can 3 digit dial back and forth. Am I correct in my thinking that if I dial a toll free number that takes me to site A, I should be able to hit an extension at either site B, C, or D and get through? It works when I dial the main site, but one of the smaller sites, not so much. Any thoughts or suggestions?