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are required by federal law to get a warrant issued by a court to tap into communications systems WITHIN the US borders and that those laws do NOT apply at the point the communications system crosses the border. Also the laws ONLY affect the legality of the use of the information gathered when it goes to court.

Thus the collection of information by an intelligence agency at the border does NOT require a warrant from a court, but it's legality in a court case varies with circumstances a lot (based on past cases).

As to 911 - there is a hell of a difference between having intercepted information and understanding what it means or where events in them are supposed to happen.