AT&T Inc. (T) said on Monday delays in activating service for customers of Apple Inc. (AAPL) iPhone had been mostly resolved after the wireless company worked out the problems on a case-by-case basis.

About 2 percent of those who bought iPhones since they went on sale Friday faced delays in activation with AT&T, the exclusive U.S. service provider for the widely anticipated cell phone, according to a source familiar with the matter.

By Monday, those issues were mostly resolved, AT&T spokesman Mark Siegel said.

"We have resolved nearly all of the issues and we feel confident this is behind us now," Siegel said. "One by one, we worked to resolve (the problems) and now nearly all of them have been resolved."

Activation delays stemmed from large customer volumes and problems with customers trying to transfer corporate cell phone accounts to personal iPhone service accounts, AT&T said on Sunday.

AT&T said that iPhone sales for the weekend were the strongest of any device in the company's history.

"We've sold more iPhones in the first weekend than we've sold in the first month of any other wireless device in AT&T's history," Siegel said.

Bill Shope, who covers Apple for JP Morgan, estimated in a research note that 312,000 iPhones were purchased on Friday and Saturday.

Other strong selling phones at AT&T have included the Razr phone from Motorola Inc. (MOT), which helped boost sales at both companies for years. AT&T was the first provider to sell Razr when it went on the market in late 2004.

AT&T shares closed up 35 cents, or less than 1 percent, at $41.85 in afternoon trade on New York Stock Exchange. Apple's stock was down 90 cents, or less than 1 percent, at $121.14