Application made by Toktumi, can work over WiFi, 3G, or Cellular networks using the Same number. Unlike the others, Line2 allows still can receive incoming calls, even when using a WiFi network the iPhone. It's a very interesting application to try. Line2 also supports conference calls with the number of participants up to 20 people.
Another advantage of Line2 is when a weak cellular signal is received, for example in the building, you can still receive calls and make telephone calls using iPhone WiFi. There are so many the advance features of Line2 like call waiting, call hold, call transfer, call swap and Advanced Call Control Features for VoIP calls.
How about video call? do not worry Line2 also supports the iPhone video calls, especially on the iPhone 4, which has equipped the front-facing or rear-facing cameras.
With Voip iPhone, the cost of phones calling will become cheaper. Only with the price of $ 9.95/month, includes Phone Number, Voicemail, Unlimited US/Canada Calling, and Unlimited Texting. This is the cheapest price than that offered by competitors.