If the two companies have indeed signed a contract — something the Journal‘s sources could not confirm — it would be the biggest carrier agreement Apple has ever struck.

China Mobile is the world’s largest phone company, with 740 million mobile subscribers. That’s about seven times more than the subscriber base of Verizon (VZ), the largest U.S. carrier.

Meanwhile, Bloomberg reports that Apple has also reached an agreement with NTT DoCoMo (DCM), Japan’s largest carrier with 60 million mobile subscribers.

Apple has scheduled a special event for Tuesday, Sept. 10, where it is widely expected to unveil two new iPhones: a so-called iPhone 5S, offering incremental improvements over last year’s model, and the lower-cost iPhone 5C that the company is reportedly shipping to China Mobile.

But the announcement of two huge carrier deals and the release of iOS 7 — the first major redesign of the company’s mobile system software since the original iPhone — could be just as important for Apple as it battles Samsung and Google’s (GOOG) Android for control of the global smartphone market.

UPDATE:  KGI analyst Ming-Chi Kuo is telling clients that China Mobile may delay deployment of the new iPhones until the company has rolled out more of its fourth generation TDD-LTE network. According to AppleInsider, that could push the carrier’s iPhone 5C launch into November.