A recent study by Consumer Reports regarding wireless service finds that the Cingular merger has not succeeded in increasing customer satisfaction. Cingular/AT&T still ranks near the bottom of all wireless carriers. See Consumer Reports Ratings for Cingular for more information.
As a previous AT&T subscriber who has switched to Cingular, I can confirm that the service has gotten worse. I now get 4 or 5 network unavailable warnings a day while trying to make a phone call- before the merger this was extremely rare. More dropped calls.
One might think that combining the networks would yield better performance, not worse. The article believes that the Nextel Sprint merger will yield worse results due to the incompatible technologies.