Apple has signed a deal with China Mobile, the world's largest mobile carrier, to offer its iPhone. The deal will give Apple access to 700 million customers, and if all goes according to Apple's plan, a big sales boost along the way.

The news was reported by The Wall Street Journal, which says China Mobile will introduce the iPhone alongside its new 4G network at a conference on 18 December. 

As Apple has struggled to gain market share in China against rivals, many have questioned why the company has waited so long to ink a deal with the largest carrier worldwide. To offer a little perspective, China Mobile is seven times the size of Verizon Wireless, the largest US mobile carrier.

The iPhone 5S and iPhone 5C released in September added network compatibility with China Mobile's unique TD-LTE and TD-SCDMA networks. The number two and three carriers China Unicom and China Telecom have been offering the Apple-line for some time.

Read: iPhone 5S review

The deal will mean big business. Analyst Amit Daryanani of RBC Capital Markets said in a note directed to investors this week that Apple will garner another $9 billion to $10 billion in annual revenue from a deal with China Mobile.

“In terms of geographic distribution, we saw highest growth in China, and it was into the triple digits,” Apple CEO Tim Cook said in January, indicating how important the region is to Apple.

Over the years it's been reported that 42 million subscribers chose to buy an iPhone off-contract through a third-party and then use it on China Mobile. Those customers are subject to 2G speeds, thanks to older iPhone network compatibility.

Soon customers will be able to buy the smartphone directly through the carrier, and we'll see Apple's revenue rise in the process.