Cingular will give you the unlock code if you just call and ask them for it. They'll send it to you within 5 days via SMS.
The catch is that "you have to be with them for 3 months with your account in good standing" from what people tell me over and over. I don't know if that means you have to have THIS phone for 3 months before they'll give it to you or if that means you have have to have been a Cingular customer for 3 months.
So just call and ask for the "subsidy unlock code."