KDDI Corp. will offer an e-mail service based on Google Inc.'s Gmail, expanding an existing alliance to win customers in the $75 billion wireless market, KDDI said Monday.

The service with Google, the world's most popular search engine, will be available in September for free, KDDI said. Users will get 2 gigabytes of storage and an auone.jp e-mail address, Makoto Takahashi, KDDI's associate senior vice president, said at a briefing in Tokyo.

KDDI, Japan's second-biggest mobile-phone operator, plans to lure users after gaining fewer subscribers than smaller operator Softbank Corp. for the second straight month in June. Since 2006, KDDI's handsets have offered Google's search box, which shows results and advertisements related to users' keywords.