I don't own the phone or have Cingular service, I have T-Mobile in NYC. But based on the bands that the phone operates on (900/1800/1900) the phone will only get about half the reception on the Cingular network whereas the phone would work well on T-Mobile. Cingular predominately runs on the 850mhz band and a little on the 1900mhz whereas T-Mobile was built on the 1900mhz network and has roaming agreements on the 850mhz network.
I just got this phone for Cingular service in the San Francisco Bay Area. Reception is typically very good; however, when I am at my desk at work the reception is very low which seems to eat up the battery life... I bought this phone to replace my Treo 650. the Treo 650 gets about 3 bars at work whereas the x820 gets 1 bar.