Another set of figures released today underscores how social networks have grown in the mobile space, this time from M:Metrics.  In total 12.3 million people said they accessed a social network on their mobiles in the month of June—although there is no mention of what kind of growth this number represents. The countries covered in the research were the U.S., U.K., France, Germany, Italy and Spain, and here are some of the other findings ( release ) :

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—MySpace was the most popular social networking site in the U.S. and U.K., attracting 3.7 million U.S. and 440,000 UK mobile users. Facebook ranked number-two in both countries, with 2 million and 307,000 users, respectively. YouTube had 901,000 mobile visits in the U.S., while in the U.K. Bebo was the third-most popular site with 288,000 users in June.

—The U.S. had the highest proportion of mobile customers using social nets in the month—3.5 percent, which works out to 7.5 million.

—Something to make the operators smile: in the U.S. and U.K. there is a strong correlation between popularity and being on-portal. MySpace has deals with AT&T, Helio, Nextel and the now-defunct Amp’d in the U.S., and Vodafone in the U.K. Facebook is on Sprint, AT&T, Virgin and Amp’d portals.

—More off-portal activity is emerging. The most popular mobile social net in France, Germany, Italy and Spain is MSN’s Live Spaces, which is only available off-portal. T-Mobile noted in July that accessing social networks off-portal was driving usage of its web’n'walk flat-rate Internet access service, which T-Mobile predicts will have 1 million users by the end of 2007.