Line of site, each handset can get up to 600 feet.
Any handset can only intercom with one other handset.
When a handset is on a telephone line, that line is inaccessable to all other handsets in the system. Another handset can be conferenced in, if desired, but it has to be initiated by the originating handset. If no numbers are pressed, or if clear is pressed, the handset returns to an idle state with the caller staying on hold. There is a hold reminder that will remind the users of calls on hold. The same 4 lines need to be continuous throughout the system.