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They never seem to get it done in time, but tracing an important phone call is key when pursuing a fugitive/rogue agent/super villain.
In real life, 911 operators and some government agencies can read your phone number as your call comes in and track down your current location almost instantly, especially with modern-day technology. Many cell phones now come with a chip that can be used to triangulate your position via GPS. Especially useful if you are trying to make a call to the authorities and get cut off or are unable to speak for some reason, or if the authorities have authorization to tap your phone.
Of course, that wouldn't build up too much drama in movie world, so often the computers in various films take a very long time to triangulate someone's position if they call in, no matter if a pay phone or a cell phone is being used, and usually the caller disconnects the phone before the computer is able to finish locating his position. All that RAM available to the computer, and it still takes several minutes just to pinpoint the caller's location...