Updated

Sprint Nextel Corp (S), which recently launched an advertising campaign to attract new customers, is disconnecting more than 1,000 subscribers for calling its customer service lines too often and making what the company called unreasonable requests.

The No. 3 U.S. wireless provider with 53 million customers said Monday it started sending service termination letters on June 25. Sprint said the cancellations involved 1,000 to 1,200 customers who had called the company about 40,000 times a month in total.

"These customers were calling to a degree that we felt was excessive," said Sprint spokeswoman Roni Singleton, adding the company needed to cull its customer base to improve services.

"In some cases they were calling customer care hundreds of times a month for a period of six to 12 months on the same issues even after we felt those issues had been resolved," she said.

Singleton, noting that mass cancellation letters were not routine, said this call volume was 40 to 50 times more than average customer monthly calls. She would not say how often customers can call before being deemed too demanding.

The company also declined to say what percentage of monthly service calls the 40,000 figure represented.

Singleton said some of the cancellations involved customers who repeatedly asked for information about other people's accounts.

Sprint waived final balances on canceled accounts and gave customers 30 days to transfer their phone numbers to other wireless providers, she said.

"We're working very hard to improve customer service. That's our number one priority," Singleton said.

The termination letters started going out days before Sprint kicked off a nationwide "Sprint Ahead" ad campaign on July 1. Sprint's customer growth has disappointed investors for several quarters after its marketing message was criticized as being confusing and it had network problems after its 2005 purchase of Nextel.

Providers AT&T Inc (T) and Verizon Wireless, a venture of Verizon Communications Inc (VZ) and Vodafone Group Plc (VOD), were quick to point out differences between their policies and Sprint's, saying they very rarely cancel services.

AT&T, the U.S. wireless service with the greatest number of subscribers, sometimes cancels or restricts services for customers for "excessive data or voice roaming on other carriers' networks," according to spokesman Mark Siegel, who said competitors had similar policies.

Tom Pica, a spokesman for Verizon Wireless which is second to AT&T by number of customers, said his company sometimes cancels services for callers who are "extremely abusive" to its customer service representatives. But, he said, this would be handled on a case-by-case basis.

Sprint shares were down 32 cents at $21.55 on the New York Stock Exchange early Monday afternoon.