NEC 28i System Manual page 46

Room to Room Call Restriction
Room to Room Call Restriction prevents guests in one room from calling
guests in another. You'll find this restriction handy for guests that want to
maintain their privacy. On the other hand, you may want to allow inter-
room calling for families or groups that have separate rooms.
When first installed . . .
Room telephones are not restricted from calling other room tele-
phones.
An extension cannot enable Room to Room Call Restriction for a
room telephone.
If you enable Room to Room Call Restriction for a guest's
phone, neither you nor any other Hotel Mode extension can
call them while they are checked in. To call the guest's
phone, first dial 136 to cancel the restriction. This may have
implications in emergency situations.
Note: Checking out a room (by dialing Service Code 139) automatically
cancels Room to Room Call Restriction.
2-38
WARNING
Help your
guests keep
their privacy
by avoiding
nuisance
callers.