Willcom Inc., Japan's largest personal handy-phone system company, said Tuesday it will introduce a flat rate for voice communication starting May 1, becoming the first domestic wireless carrier to provide such service.

PHS is a no-frills mobile phone service originally developed in Japan. But its shrinking subscriber base prompted NTT DoCoMo Inc. to ease out of the business.

Willcom, a wireless carrier dedicated to PHS, expects to boost its subscriber base to 4 million with the flat-rate program, up from the current 3 million.

It said the service will allow users to call fellow Willcom PHS users for unlimited minutes for 2,900 yen per month.

Willcom CEO Yoichiro Yatsurugi told a news conference the firm expects the subscriber increase to more than offset a projected fall in average revenue per user with the introduction of the flat rate.

In addition to corporate users, the company said it will target users who make long calls to certain numbers, including dating couples.

Although the flat rate is applicable only for calls among Willcom subscribers, Yatsurugi said the company is already in talks with land-line operators about the possibility of a flat rate for Willcom users making calls to these services.

Willcom, formerly DDI Pocket Inc., was bought out from KDDI Corp. by the U.S. investment firm Carlyle Group.