PORTLAND — Sprint Nextel Corp. will offer Apple’s iPhone next month with unlimited data service plans to distinguish itself from rivals AT&T and Verizon Wireless, according to people familiar with the matter.

Sprint, the third-largest U.S. wireless carrier, plans to begin selling the device in mid-October under a deal with Apple for the next model, the iPhone 5, said the people, who wouldn’t be identified because the plans aren’t public.

Becoming the country’s only operator to offer the device with unlimited data service for a flat fee may help Sprint draw customers from AT&T and Verizon Wireless, which already carry the phone, they said.

Sprint, based in Overland Park, Kan., is struggling to compete against larger rivals and has lost money for 15 consecutive quarters. The addition of the iPhone to Sprint’s lineup will help it win customers, said Matthew Thornton, an analyst at Avian Securities.

— From wire reports