Sierra Mercury: AT&T's Smallest, Sveltest 3G Data Card Sierra's latest USB 3G data card, Mercury, is the smallest, smokiest little card in AT&T's otherwise obese lineup. Obviously spawned from the same DNA pool as its Sprint-y cousin , but with the chrome and black look AT&T is fond of lately. Like the Compass, the drivers and AT&T's software are loaded on the stick, so you don't need a CD to install it, and it has a microSD slot. Theoretically, it should deliver the same excellent performance. Better still, it's free with a two-year contract. [AT&T , AT&T ]