Facebook Zero, the cut-down version of the social networking service that comes without data costs, has been launched in 45 countries with the UK to be added soon.

Facebook Zero is a text-based version similar to the existing Facebook Mobile but with one key difference - users don't have to pay for the data used to access the service, until they click on a picture or video.

That free data is only possible by arrangement with network operators, and only with network operators whose billing systems are up to it, but more than 50 have signed up at launch.

When the service was announced the focus was expected to be on countries where mobile broadband is still developing, but while those countries are very much in evidence they are joined by those with more developed wireless infrastructure: Belgium, Hong Kong and Denmark for example, with the UK, France and Australia soon to be added.

In the UK 3 is the first to commit to free access for punters wanting to access 0.facebook.com, though we don't know the details of how that deal will be made available yet.

Facebook isn't paying the operators for the bandwidth: the idea is to reduce the overall network loading to the benefit of all (though particularly to the benefit of Facebook, obviously). Users can get their news feeds, send and reply to messages and interact with contacts' walls, all without charge, and without pictures too.

Click on a picture and you're into chargeable territory, the price being dependent on your data tariff. But by offering a free hit, Facebook operators will be hoping to seduce users into becoming addicted to live updates from their social network: before they know it they'll be frolicking on Farmville and running up huge data bills. Hurrah. ®