If you’re a Vopium user, or perhaps a wanna-be Vopium user because you have an iPhone, you’re in luck as they recently released the free iPhone app. More about the Vopium VoIP mobile service.
It integrates tightly with your iPhone contacts directory so you can quickly make VoIP phone calls. You can trial Vopium for free as new users are given 30 free minutes of talk time and 30 free SMSes.