By now you're probably aware that Skype video calling over 3G is possible, but do you know how much of your data plan the new feature is using up?

Probably not, but you'll soon find out if you over use it and you get a hefty bill from your mobile network provider.

Luckily though, fanboy bloggers 9 to 5 Mac has done some testing, and has come up with the figure - it's 3.4MB per minute.

We don't think that's too bad. To put it into perspective, if you're on O2 and you get 500MB a month in your data plan, you'll be able to make almost two and a half hours worth of 3G video calls per month (if you don't use your data for any other reason that is).

Still, even with daily browsing and downloading over 3G you'll still probably be fine with around an hour or so of 3G video calling, which should be enough considering no-one even wanted to make video calls a few years ago when we first had the chance.

Neil Stevens, general manager of Skype’s consumer business thinks that the demand for video calling will continue to grow, however.

"With video calling representing approximately 40 per cent of all Skype-to-Skype minutes for the first six months of 2010, our users have been eager to get Skype video calling on their mobile phones," he said.

"By bringing video to mainstream users at their home or work via their desktops, on the go with their mobiles, or into their living room via their TV, Skype has made it possible for millions of people to share video moments wherever they are."

Skype 3.0 is out now, for free, in the App Store.

See also - Skype iPhone video calling hands-on