When you're racing to get something done on a deadline and you get interrupted by a long-winded caller, do you:
(a) Let them talk, trying to politely hint that you don't have much time
(b) Say, "I'm actually short on time right now. Could I call you back?"
Far more people do (a) than (b) -- because people want to be nice and aren't sure how to nicely protect their time, or if it's even possible to do it nicely. It seems to me that people often get so focused on wanting to be nice to the long-winded caller or visitor that they forget that -- when at work -- we have a larger obligation to use our time in the ways that are most effective. And yes, it can be done without being rude. Here are some principles to use (all of these assume that your job isn't to take long-winded people's phone calls):
1. Your obligation to the long-winded caller is to be polite as you're ending the call, but it's not to allow them to cut into time that you could be better spending on something else.
2. White lies are made for this situation. Say "I've got to run to a meeting that's about to start" or "I have someone standing right here waiting to talk to me" or "I've got to grab this other call coming in" or "I'm on deadline" or whatever. If the person ignores you, repeat it again firmly -- right away, not after letting them go on for another five minutes.
3. Set a time limit for the call at the very start, such as "I've only got a minute to talk" or "I appreciate the phone call but only have a second to talk."
4. If the above doesn't work, don't be afraid to interrupt a long-winded person who doesn't pause to take a breath or let you get a word in. Remember, you are responsible for how you spend your time; they don't control it.
5. If the interruption is in person and the interloper won't leave your office, stand up with some papers in hand. Sometimes this alone signals that you have something else to do. If the signal doesn't take, say, "I've got to run these down the hall."
The general idea that you should take control of your own time applies in other ways too: For instance, if you're a manager who finds it hard to focus because an employee interrupts you with questions throughout the day, ask the person to save up their questions and ask them in bunches. Or if someone asks you to do something right away that's less of a priority than what you're working on, say "I need to finish this first, but I'll get to it as soon as I can." (Although if it's your boss, reword it to: "If I do this immediately, it'll delay X"; this gives her the chance to tell you that X is less important after all.)
The key point is to be nicely assertive and not let others control your day.