We've recently released a free SIP based VoIP Client and Softphone for android mobiles.
It Enables you to make Free VoIP Calls to anywhere in the world.
We believe it's very easy to configure and we need to get feedback from market on it.
To test it:
You'll need a SIP Account, If you don't have one go to http://iptel.org and create one.
Download the app from the market, http://goo.gl/zJPuL
Enter your account's user and password in the settings
Restart the app
Congratulations, you can now call other VoIP numbers anywhere in the world.
Waiting for your feedback to enhance the beta.
Thanks in advance