For my wife and me, the third biggest disappointment of coming back to the States from Japan, after not seeing family as often and changing our diets, was giving up our mobile phones. Our phones may be a distant third on that list, but it says something that they even warrant a mention.

In the U.S., having a mobile phone is very convenient, even a necessity for some folks. And while usage of the Internet and other services via mobile phones is increasing in the U.S., it's a way of life in Japan. In the same vein, having a website in Japan is great, but having a site that's also available via NTT DoCoMo's (NYSE:DCM) i-mode or Au's Ez-Web is very important as well.

This brings us to DoCoMo's announcement today that it will purchase a 40% stake in Rakuten's Internet auction spinoff, Rakuten Auction. Rakuten is Japan's largest online shopping mall operator. The combination of Rakuten's online sales capabilities and DoCoMo's position as Japan's leading wireless carrier is an intriguing combination, particularly since it should yield plenty of well-placed links on the web pages that DoCoMo's i-mode users are directed to.

DoCoMo's involvement should help Rakuten Auction more effectively compete against Japan's current king of Internet auctions, Yahoo! Japan (NASDAQ:YHOO). Yup, you heard right -- Yahoo!, not Motley Fool Stock Advisor pick eBay (NASDAQ:EBAY), is king in Japan. eBay never got a footing in Japan and eventually threw in the towel a few years ago.

Whether Rakuten Auction can overthrow Yahoo! Japan is debatable, but given how often mobile phones in Japan are used for browsing online, playing games, and sending text messages -- things we generally associate with PC's here -- DoCoMo's ownership stake can only help improve Rakuten's chances.

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Nathan Parmalee has no financial interest in any of the companies mentioned. The Motley Fool has an ironclad disclosure policy.