Fring, the  instant messaging app that lets you manage your Skype, MSN and AOL accounts on your iPhone has confirmed that users will now be able to make VoIP calls over the 3G network.

The move, which has been made possible due to a change in rules in the latest Apple iPhone SDK released on Thursday, could spell trouble for the operators as there is a potential for people to now bypass the need for making lucrative international calls as part of their call package.

AT&T in the US, for example bars new customers making such calls for the first 3 months of a new contract suggesting this could be the lifeline they are looking for to make calls on the cheap or for free.

Skype, however, has yet to announce that it will be offering 3G calling from within its dedicated app.

Fring says current users won't have to download any new software, however do state that if users are experiencing difficulties using the new feature that they should log out and then back in again.

Having the chat application running in the background, however, is still beyond the realms of what is capable for the iPhone unless users jailbreak the handset.