To call someone on a cell phone in order to locate where they are. Usually done when you are at the same physical location and uses the conversation to close in on the person you're trying to find.
Just a second, let me cellpholocate Joe.
Ring... Joe, I'm at the theater, where are you? You're standing by the entrance? What are you wearing? You wearing a blue jacket? Stick your arm up so I can see you. There you are!