Sprint Nextel Corp. is set to become the second U.S. mobile-phone carrier to offer Apple Inc.'s iPhone on a pay-as-you-go basis.

Sprint will announce this week it will offer the popular smartphone on its Virgin Mobile pay-as-you-go brand as soon as July 1, according to people familiar with the company's plans. The Overland Park, Kan., carrier follows Leap Wireless International Inc. in selling the device with prepaid service.

Offering...