Softbank Corp., Japan's only provider of Apple Inc.'s iPhone, is losing part of that exclusivity as Japan Communications Inc. starts offering chips that will allow the smart phone to access another network.

Japan Communications will offer a subscriber identity module, a chip that allows unlocked iPhone 4s to use NTT DoCoMo Inc.'s network, Japan Communications said Monday.

The service will cost ¥5,280 a month for unlimited data use with a separate charge for voice calls and will be available starting Thursday for users who reserved online, according to a statement by the closely held company.

Softbank remains the only carrier that sells the iPhone in Japan, where handsets are locked, meaning they don't accept SIM cards from other providers. Japan Communications' SIM cards will work with unlocked iPhone 4 models that can be purchased online or outside Japan.

Japan Communications offers mobile phone services by leasing a portion of DoCoMo's network. The company's iPhone plan also allows users to connect a laptop to the Internet via the smart phone, a service not offered by Softbank.

Japan's smart phone shipments will probably exceed 3 million units this business year, which started April 1, while the overall mobile phone market is expected to contract for a third year, according to MM Research Institute Ltd.