AT&T Inc said on Monday delays in activating service for customers of Apple Inc.'s iPhone had been mostly resolved after the wireless company worked out the problems on a case-by-case basis.

About 2 percent of people who had bought iPhones since they went on sale on 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, these 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.

The iPhone went on sale across the United States on Friday, attracting thousands of buyers at Apple and AT&T stores. After the purchase, customers had to log on to Apple's iTunes online store to activate the service.