The area might not be important, because we don’t know when and where the attack will take place. It may have simply been a convenient place to buy cell phones, because of the relative remoteness of the location, as opposed to buying them in New York or Los Angeles.
However, obviously they bought them for coordination as well as ignitions.
They are for communications. Burners to use several times then toss. Numbers are being passed discretely to cell members via simple coded posts on the net.
ME terrorists use cell phones due to lack of alternatives in their desert 3rd world. Not the case in this country. Far better equipment is available here thanks to the techno crazy American culture.