It has ATT firmware.  Because it is unlocked, it accepted your Cingular SIM.
Nothing at all to worry about, as long as you have verified that you can
make and receive phone calls with it.  -Dave

I have one that came from France and one from Switzerland.  The French
one says AT&T when I am on using the network that still has the old
AT&T network codes (MNC).  The other one says Cingular and shows the
roaming triangle.

The difference in my case is that the French RAZR is slightly older
and the firmware in the phone associates the MNC with a label of AT&T.
The newer RAZR was sent with the new labeling.