NTT DoCoMo and Internet shopping mall Rakuten would offer online auctions for personal computers starting this week and for mobile phones from November 20, a Reuters report said.
The Reuters report said the two companies will also offer a social network service as part of the tie-up announced last year, in which DoCoMo would take a 40% stake for 4.2 billion yen ($36 million) in a new company, a spin-off of Rakuten's auction business.
The alliance challenges Yahoo Japan, the country's most popular Web site and biggest online auction provider, as well as DoCoMo's smaller mobile phone rivals KDDI and Softbank, which are offering new services such as digital TV and music downloads to lure users.
Yahoo Japan is owned 41% by Softbank and 33.4% by Yahoo of the US.
Softbank also owns Japan's No. 3 mobile phone carrier.
Rakuten, whose services range from online shopping, travel booking and brokerages, is also in prolonged talks with Tokyo Broadcasting System for possible alliance in areas such as Internet TV and e-commerce after Rakuten dropped its takeover attempt last year.
DoCoMo is also seeking to spread its so-called 'wallet phone' service, which allows consumers to use their phones as debit or credit cards, to drive revenues and retain customers.