the KDXG only has 3G/2G, so far from looking at the FCC ID and specs, no hardware support at all for wifi
so you can only use cellular connection for internet... you can still transfer files via USB
you sure you don't have ANY at&t signal at your place? 2G/EDGE still might work, at lower speeds
microcell requires you to have a plan imo, since whenever you use it, the minutes still get deducted from your plan even though the traffic goes over your broadband...