I was looking at your profile when I was reading your question about connecting Norstars in the Nortel networking solutions, and found this question.
Regarding this one: If you don’t need those phones to receive internal calls either, you could put them on DND, and then change the set lock setting for that DN to “Full.” Once the set lock is enabled, they would not be able to disengage DND. Of course they would not hear internal calls ring either.- If that is a problem, you could set up an overhead/ horn paging system so that if you needed to talk to one of the employees at those phones you could page them to call you at extension XXX, instead of dialing them directly.
Regarding your other question about connecting two Norstar systems together: That is some advanced stuff, and I would definitely recommend getting an experienced vendor involved. I also think you might get more responses if you post it here, instead of the Networking forum.