Tuitalk
Tuitalk is a free Voip client made by Argela. It allows users to call landlines and mobile phones via Wi-Fi. And, you are not asked for a credit card number. The application was released in 2008 for Windows and Mac OS X.
While the call was being made, the program shows a video ad before the call starts ringing. You can make only 3 calls a day, everyday for free.
Computer release
The release of Tuitalk for Windows and Mac was in 2008 as a free download. When you first start it up after you make an account and download Tuitalk, it will ask you to log in. Once you log in, you can start calling people. Tuitalk is no longer working in US.
iOS version
The iOS version of Tuitalk was released for the App Store in June 2009. It is just about the same idea as the computer client. It uses a keypad for number dialing on the touchscreen. IPod touch users must have a microphone plugged in to talk.
On April 1, 2010, Tuitalk became available for the iPad tablet.