AT&T and Cingular System ID's

My phone (a TDMA Nokia 6560) has always shown AT&T on the main display when the phone is in idle mode. Today my phone began showing 'Cingular' on the display. When I went to the network monitor screen, sure enough, it now shows system 4105 Cingular. The conversion is in progress. In the near future, it will be worth it to switch to GSM, as the GSM side becomes more robust, and system resources