Phweet is a recently launched startup that enables the already chitchatting twitterians to go vocal, i.e. have conf calls with your tweet friends.
Once you signin, you can send the PhweetURL via Twitter and your Twitter Followers can join the conf call(i.e. Phweetup)
I have covered the TringMe’s VoIP API earlier (read how one can easily build own Mobile VoIP solution); and as Yusuf tells me, this is just the beginning of their journey – TringMe is announcing few more partnerships in the coming days – UK/Brazil based social networking company, ex-MIT startup and a Chinese social network.