When Kimberly Randolph, an operations supervisor for the Sprint phone company in Kansas City, Mo.

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"Well, I've been in (law enforcement) for over 20 years, and it seems like within the last five to 10 years they have gotten really, really creative in how they bring their drugs across, " said Andy Adame, special operations supervisor for the Joint Field Command Arizona of U.S. Customs and Border Protection.

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Though the disputes--most commonly customers arguing with collectors about change-- occur about once a week, Olga Krueger, the supervisor of bridge operations, says she hasn't seen a robbery during her six-year tenure.

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