Just got the AT&T 4S. I'm seeing the same problem with Speck Pixelskin reviewer had with a Verizon 4:
... I bought this cover for a Verizon iPhone 4 and the cut out for the ring/vibrate switch does not fit. It may be fine for the ATT phone, but not Verizon. It is advertised as fitting both, but it makes it look like the cover doesn't go with the phone...
On our new 4S the mute switch slot is too high. I wonder if the AT&T 4S more closely resembles the Verizon 4. Many cases will have similar issues.
I'm disappointed that Speck is marketing their cases as 4 and 4S.