More than a quarter of Facebook’s users are accessing it through mobile devices every month, and the number of mobile useres is growing fast. But not every Facebook user has a good mobile data connection, or a mobile data plan.

So the company has been working on a simplified mobile site that loads faster, in part by minimizing some features. In partnership with 50 carriers in 45 countries, access to the site is free, even if users don’t have an existing data plan with their carrier.

The site, at 0.facebook.com, is launching today. See the current list of carriers and countries, below.

It lets people do basic things like read their news feeds, publish status updates and wall posts, and like and comment content. But, if users want to access some parts of Facebook, like Photos, they’ll have the option to click through, pay for the data service, and view the content. While Facebook can provide its service for free to mobile users, carriers can make money by the site’s features enticing people to pay.

The “0″ site follows on other efforts to make Facebook more accessible to users, including a now-defunct “Lite” web site and other mobile integrations with carriers. Check out our recent article on the topic, available in our Inside Facebook Gold membership service.