Fox Media’s social networking monster, MySpace, has opened up its mobile offering to all and sundry.

As of Tuesday, the MySpace Mobile Web beta service has been live and serving ad-supported content, marking the first time that Fox has delivered an advertising platform to marketers looking to reach mobile web users.

To date, MySpace has only been available to mobile users via tie-ups with local operators such as AT&T, T-Mobile and MVNO Helio in the US and even then the service has been tailored for specific devices. But MySpace has been coming under increasing pressure from rival social networks such as Facebook, which have more readily adopted to the mobile platform.

Figures from Nielsen/NetRatings show that Facebook recently overtook MySpace as the most popular social networking site in the UK but also noted strong growth from the likes of Perfspot and Bebo.

“The MySpace Mobile Web significantly lowers the barrier of entry for all MySpace users to access their profiles on-the-go,” said Amit Kapur, VP of business development for MySpace. “An ad-supported MySpace offering is a major component of our mobile monetization strategy and we look forward to broadly offering this industry leading roll-out to advertisers.”

Fox has partnered with mobile ad network Millennial Media to sell and serve mobile-based ads. MySpace Mobile’s free functionality includes the ability to send and receive MySpace messages and friend requests; comment on pictures and profiles; post bulletins; update blogs; find and search for friends; and view or change mood status.

As if more evidence were needed that social networking is the ‘Next Big Thing’, Microsoft is reportedly ready to buy a 5 per cent stake in Facebook for between $300m and $500m.

If that number is accurate it would value Facebook at up to $10bn and make its founder, 23 year old Mark Zuckerberg a very happy man.