Peter Sisson, the founder and chief executive officer of Toktumi, a San Francisco-based VoIP startup, is elated. He was jumping with joy when I spoke with him earlier today. Why? Because Apple just approved the latest version (2.0) of his company’s mobile VoIP app, Line2. The app, which costs 99 cents, allows you to call and receive phone calls over both 3G and Wi-Fi networks.

What Toktumi has done is build a back end similar to that of Google Voice — but unlike Google, it’s gotten Apple’s blessing. It’s one of the more complete mobile VoIP apps currently available for download; I especially like the fact that it allows you to receive calls straight to your mobile phone over a cellular network even if you don’t have 3G or Wi-Fi coverage. It comes with its own features such as call waiting, conference calling, call transfer and even voice mails — in other words, the service is like a virtual second line on your phone. The service costs $14.95 a month for unlimited calls in the U.S. and Canada.

Toktumi, which launched at DEMO 2008, has had to traverse a difficult path to get to where it is today, and Sisson is understandably excited about the kind of exposure the approval from Apple of its app will bring. Sisson, a veteran of the VoIP business, sold his last company, Teleo, to Microsoft.