Softbank’s reign as the exclusive provider of the iPhone in Japan is to end after Apple confirmed that rival KDDI will join the operator in selling the newly announced iPhone 4S.

Speculation of this development has been rife for a while, as we reported back in September when KDDI took down its Android website ahead of expected iPhone developments.

Softbank is one of the few global operators in a primary market to enjoy an exclusive hold of the iPhone, a factor that has given it significant traction in the Japanese market.

Since Softbank began carrying the iPhone, with the iPhone 3G in 2008, it has steadily gained ground on KDDI, with projections showing it close to eclipsing the older carrier’s subscriber numbers.

history 520x228 KDDI to get iPhone 4S, end Softbanks exclusivity in Japan

There is no development on iPhone for Japan’s number one operator NTT DoCoMo, represented by the grey line in the chart above (Softbank is blue, KDDI red). Though it doesn’t offer the device itself it does support iPhones that transition onto its network from Softbank.

The introduction of the iPhone 4S to KDDI customers is likely to bring about greater competition – particularly around quality of service and pricing – as KDDI increases the heat on its rival. Currently, around half of Softbank’s new customers are believed to be signing up for iPhones,  a statistic that is likely to change very soon.

There is still no word from Apple on China Mobile, the other major Asian operator strongly speculated to begin offering the new device. Give its 600 million plus subscriber base, China Mobile could be a key ally in China – a market where Apple is beginning to defeat the counterfeit phone culture that plagued smartphone development in the past.