Currently there are two carriers in Japan that sell the iPhone, which includes KDDI and SoftBank. NTT DoCoMo, the largest carrier in Japan, will start selling the iPhone this fall.
It was reported that NTT DoCoMo was losing many subscribers because they were not offering the iPhone.
NTT DoCoMo reportedly held off from selling the iPhone because of the obligations that they would have to pay Apple when carrying the device. NTT DoCoMo also wanted to preload certain apps on the iPhone.