The two companies are discussing offering Google's Map for Mobiles on Tokyo-based NTT DoCoMo's i-mode handsets, and plan to explore ways to make it easier for users to access Google's e-mail, YouTube and other services, they said in a statement.

NTT DoCoMo's i-mode technology is how its cell phones link to the Internet.

Google search results will appear by default on the handsets' search portal page starting in spring 2008, the statement said. Keyword-based advertisements will also appear on search result pages through Google's AdWords advertising platform, it said.

DoCoMo is studying as well the possibility of introducing to the Japanese market handsets that will use Google's "Android" mobile software package, it said. Google's long-anticipated cell-phone operating system is expected to be available the second half of this year.

NTT DoCoMo had nearly 53 million subscribers and commanded more than half of Japan's mobile phone market at the end of September. It has struggled to add new users in recent months amid fierce competition from KDDI Corp. and Softbank Corp., which have slashed rates and launched aggressive sales promotions.

For Mountain View, California-based Google Inc., the alliance will give the company better access to the Japanese search engine market, Japan's leading business daily the Nikkei said in anticipation of Thursday's announcement. Although Google is the world's leading search engine, in Japan it lags behind Yahoo Japan Corp.

Mobile service subscriptions exceeded 100 million in Japan as of the end of last year, with some 70 million users accessing the Internet through their cellular phones.

NTT DoCoMo's stock rose after the company announced plans to disclose a brief on the deal after the close of trade on the Tokyo Stock Exchange. Its share price gained 3.2 percent to finish at 161,000 yen (US$1,511; euro1,037).