a few years ago, i worked at a company that had a seimans phone system that was customized to make it unique (at the time) all the "desk" phones automatically "rolled over" to a hand held portable devise (smaller than a cordless, but bigger than a cell phone) In order to 'answer' a call at your desk, you had to reroute the call back to your desk.

they didn't have a huge range horizontally, they just worked in the office. and just barely in the mens rooms or ladies rooms just out side the office..

but they did work vertically.. so if you went outside to have a cigarette, and remained close to the building (and on the side our offices were, the phone worked..(4 floors away, and they also worked in the NYSC (sport club/gym) 2 floors below us...
so some employees took to taking extended lunch hours, and working out in the gym.. but they could still answer there phone... if a boss was looking for you, and could find you in the office, you could lie and say, oh, i am in the ladies room..