Cingular in Pittsburgh

Yes, factory unlocked phones are fine for using with Cingular SIMs. It sounds as if you are considering a phone with with only 1900 MHz for North America (probably include 900 and 1800 MHz for overseas, therefore a TRIband).

Don't do it--get a phone with both 850 and 1900 MHz for Cingular. Another kind of triband is 850/1800/1900 MHz, this would be fine also. The original cellular system Cingular is using was build by ATTWS. ATTWS likely put in some 1900 MHz GSM at the beginning of their transition from TDMA digital, but you want to be able to use the entire system.

The reason it's mentioned that the ebay phones you've looked at are not compatible with 850 MHz, is because it isn't built in!

COtech