Need something to watch on a flight? You can download an episode of your favorite show in less than a minute and a half on Verizon Wireless at Atlanta's airport-or spend 13 hours doing the same over T-Mobile USA at Los Angeles International. The comparison of 45-minute HD video downloads illustrates the wide variation in cellular service at U.S. airports, which RootMetrics laid out in a report for the first half of 2015 that's being issued Thursday.