Japan's second-largest mobile carrier KDDI will sell Apple's new iPhone, the California-based company said, ending rival operator Softbank's highly profitable reign as the sole provider in Japan.

Shares in Softbank fell 2.8 percent in early trading, while KDDI fell 0.4 percent, compared with an almost flat Nikkei average.

Softbank will put the iPhone 4S on sale on October 14, while KDDI said it has not yet decided when it will begin to offer the latest version of the hugely popular smartphone.

The move, reported earlier by Japanese media, comes after Apple opted for similar strategies in other markets, with Sprint becoming the third operator to offer the iPhone in the United States, after AT&T and Verizon.

Analysts say loss of de facto exclusivity will be a blow for Softbank, Japan's third-largest mobile carrier, which has long been criticized by users for its patchy network quality.

To lose that effective exclusivity does give them a little bit more head wind. They will have to work harder, said Nathan Ramler, an analyst for Macquarie Capital Securities.

The reception for the iPhone 4S, unveiled on Tuesday in California, was lukewarm compared with the rapturous welcome sparked by previous models.