Japan Telecom Co. Ltd. has issued options to British Telecommunications PLC that allow the company to increase its stake in three local units of J-Phone Communications Co. Ltd., Japan's number-three wireless carrier and the wireless unit of Japan Telecom, by 5 percent.

The warrants, which cover J-Phone companies in Japan's three major areas including Tokyo, expire on September 29 and allow BT to purchase the stake for 68 billion yen (US$546.2 million), Japan Telecom said in a statement.

BT is currently the third largest shareholder in the J-Phone behind Vodafone Group PLC, which owns 26 percent, and Japan Telecom, which owns 54 percent. The rival British carriers have both made clear wishes to increase their stakes in J-Phone and Friday's news is the latest stage in a story that began late last year when Vodafone purchased a combined 15 percent stake in Japan Telecom from West Japan Railway Co. and Central Japan Railway Co. In February of this year Vodafone increased its influence on the company by snapping up a further 10 percent stake in Japan Telecom from AT&T Corp., which was selling it after NTT DoCoMo Inc. agreed to take a stake in its wireless arm, AT&T Wireless Group.

At the end of March, J-Phone had 10 million subscribers nationwide putting it behind DDI Corp.'s Au service, which had 11 million, and market leader NTT DoCoMo Inc., which had 36 million subscribers, according to data from the Telecommunications Carriers Association.