The cell phone has replaced many other forms of electronic communication within our society ... the CB and/or walkie-talkies, in your case the in-house Intercom, and for some even the land-line based telephone. I know several ppl who move quite frequently (usually within NYC) and the only phone they have is a cell-phone, because their number is always constant wherever they move to, and they don't have to mess with installation and activation of new phones all the time (or new numbers and area codes).
Sometimes I'll use mine when going to see a show and have to meet someone at the theater ... one of us will call the other to give their current location, and sometimes we're standing only a few feet away from each other when the call is made, unaware that the person we are talking to is right there within shouting distance! /laughs
I’ll be out with the GF, we’re at a store, and we’re there to buy a specific thing and leave, and we’ve done that, and were heading back out to the checkout. I walk faster so I’m in front. Next thing I know she’s gone. I have to call her on the phone to find out what shiny object caught her attention, and what aisle she’s in.