As the guy who filed the FCC application for the Burning Man GSM test, I can tell you that what we
did was completely legal. Our license was WD9XKN, STA file #0353-EX-ST-2008, good for one
week in an area 10 miles NE of Gerlach, NV. We also coordinated spectrum use with a licensed
cellular carrier in the area. All of this is presented in the project web page.
What you describe is an IMSI-catcher. That's not what we were doing.