There's been considerable talk about VoIP services one the iPhone since the device's debut in June last year, and with the recent release of the beta-status iPhone SDK and Steve Jobs saying it would not block third party developers from creating VoIP solutions for the iPhone, it was just a matter of time before such applications began cropping up.
Now, fring has announced what it's calling the world's first publicly available mobile VoIP app for the iPhone - albeit an unofficial one which requires a jailbroken or otherwise hacked "open" handset. That said, the company does adhere to Apple's guidelines by using Wi-Fi for calls and is labeling this a "light, sneak preview R&D version," so an official version is still expected in a couple of months when Apple opens up to 3rd party apps.
This is certainly great news for all iPhone users out there, as fring offers some nice features including both VoIP and instant messaging through fring, Skype, MSN, Google Talk, ICQ, Twitter, Yahoo! and AIM. You can download fring here (assuming you have a jailbroken iPhone and installer.app installed), or watch a video demo here.