Yes, Cingular supports the N-Gage. The N-Gage is a tri-band GSM based phone so it is supported by T-Mobile, AT&T Wireless, and Cingular Wireless in the United States. I went into a Cingular Store and asked them about it and the guy told me that I could even get a regular montly plan without the need to sign a contract.
This new N-Gage is called the N-Gage QD, and it has a slot-loading MMC slot, no usb port, no mp3 player, no radio, a brighter screen, relocated "enter" button, and finally a front-talking design instead of the side talkin' design of the original N-Gage. I personally like the original N-Gage better because it has more features than the N-Gage QD, even if I would have to talk on the side (which is different and I think its kind of funny to watch)