Apple's CEO Tim Cook is optimistic of iPhones doing well in China as China Mobile, the world's largest mobile carrier, starts selling iOS devices Jan. 17. In a brief interview with the Wall Street Journal and other publications, Cook hinted at Apple's future plans in China and said it is only the "beginning."

Apple's deal with China Mobile is a major milestone for Cook since it took six years for the tech giant to close the negotiations. China Mobile is the last carrier to offer Apple's iPhones since the other carriers went ahead of it.

According to reports, iPhone preorders through China Mobile have already exceeded one million units. The China Mobile deal is expected to increase Apple's sales in the coming months. This is a much-needed boost for the company since its earnings growth has slowed down in the previous year.

The Apple-China Mobile deal will enable both companies to attract more customers and gain a bigger share in a market with 1.2 billion subscribers. China Mobile's retail stores are ready to sell iPhone 5C and iPhone 5S on Jan. 17. Apple's retail stores in China will also carry China Mobile-compatible phones under the multiple-year deal.

Unlike former Apple CEO and Founder Steve Jobs who was never publicly seen traveling to China, Cook visited the country three times in 13 months, according to the Wall Street Journal. He held a rare meeting with China Mobile Chairman Xi Guohua as an indication of the partnership's significance to both companies.

Cook said Jan. 17 will be a "monumental day and watershed moment." Apple has sold more iPhones in Greater China, which includes Hong Kong and Taiwan, in its fiscal first quarter ending in December. In October 2012, Apple posted fourth-quarter revenue for China with $5.73 billion, which has increased by 6 percent from the previous year.