By Harry R. Weber
The Associated Press

ATLANTA - Cingular Wireless is on the verge of becoming the nation's largest mobile phone provider with its planned purchase of AT&T Wireless, but the company must fix service problems if it wants to become an industry leader in its own right.

Both companies have lost more subscribers than they've gained under a new federal rule that allows cell-phone users to switch carriers without losing their phone number.

In its February survey of cell phone users, Consumer Reports said Cingular and AT&T Wireless trailed industry leader Verizon Communications and rival Nextel Communications on service. Cingular and AT&T subscribers suffer from overloaded circuits in several cities and have customer turnover near 30 percent annually, the magazine found.

Some worry that those problems could increase if the $41 billion deal announced Tuesday goes ahead.

Company officials and some analysts counter that Cingular, cobbled together from small local wireless carriers, has experience melding distinct networks, call centers and billing systems. The company said it has condensed more than 60 call centers into 22 and 11 billing systems into two in recent years.

"The service will get better, and I will commit to that," Cingular chief executive Stan Sigman said Wednesday. "There won't be dropping of calls. They will have good voice quality."