ZoiPer Pro – SIP Softphone for android from Securax LTD.

ZoiPer is a free softphone, which you can use to make Voice over IP (VoIP) calls through a Wi-Fi or 3G network, or over the Internet. In order to place a VoIP call through the Internet, the user needs to connect to a Wi-Fi network first.

With ZoiPer you can:

Save unlimited numbers for each user on your Android device. Place any number of VoIP calls using either of the saved numbers. Make unlimited calls to numbers of your friends, using their saved numbers, and save the number for future calls.