It took me a while to realize that calling your coworkers is only possible after you "finish" their route, because in my mind unlocking the ability to call them is part of their route, not something done after it. It would probably be good to make that a little more obvious. Maybe instead of saying it's the end of their route, say something about knowing them well enough to talk to them outside of work? Not necessarily with those exact words, but something that gets the idea across better than just saying it's the end of their route.