Cell phone snooping - Texas 7

Curious article about some cell phone snooping during the capture of the Texas 7. Not enough details to figure it out, but it seems they were setup at the roadblock to intecept cell calls. http://www.dallasnews.com/metro/270831_main_25met.ART.html What is the law on this? I thought they need a court order, and then it was only good for the specific number(s) only, and had to go through the telco switch. Didn't know they could just capture every number from a specific cell site or location. Article implies they had their own little black box at the site that recorded all calls at that location.