Similar problem as panda and clightinghorse. Hotel had room numbers 180-189. Rooms were getting calls when callers dialed 1800 or 1888. Solution we used was to create ext. 1800 and 1888 on a non equipped dnic phone. Conflict dialing handled which extension to ring. If someone dialed 1800 they received a busy. Dialed 180 and the room phone rang. One thing that bit us was the voice mail. Need to add slight delay after message waiting dial string, so switch knew what extension was to have the light turned on or off.