What is Nimbuzz?
Nimbuzz let's you connect and interact with your buddies across popular communities, including Windows Live Messenger, Yahoo! Messenger, GoogleTalk and social networks including Facebook. Call, chat, message, share files and more, with all your friends in one place.
Free calls worldwide: Instead of calling minutes, Nimbuzz uses the internet to let you make free calls to your buddies. You can also register your VoIP account to call your friends on landlines and mobile phones. All you need is an internet connection.
More info on costs.