Open source VoIP app CSipSimple is not affiliated with any VoIP provider, so it doesn't favor one over the other like Nimbuzz and fring do. Because it doesn't route your calls through its own servers it sounds a lot better than the competition. It integrates with your native dialer app unless you tell it not to, in which case it stays out. Other features include switching off your ringer when you're on a VoIP call to keep incoming calls from blowing up your ears, a clean uncluttered user interface, and support for multiple simultaneous calls.
The latest update adds a new low bandwidth codec for when you're on a slow 3G (or worse) connection. Combined with a new echo killer your calls will be friendly for your ears even if your internet is as slow as the government.
But the real big change in CSipSimple is a new set of plugins. There's a plugin for Betamax. Nope, that's not the old and extinct VCR format, but a collection of SIP providers like VoipCheap, 12voip, and dozens more. Of course you could already use all those SIP services with CSipSimple, but with the new plugins you can now also use their local access numbers and callback service. This can be useful if your mobile carrier doesn't allow you to use classic VoIP over their data network or if you're about to hit your data limit.
The other plugin is for Skype. This first version just launches the Skype client if you pick a Skype contact from CSipSimple, so you need to have the official Skype app installed on your phone. Maybe one day CSipSimple will add the Skype support that Nimbuzz and fring had to drop?
• CSipSimple (Google code)
• CSipSimple (Android Market)
• CSipSimple Betamax plugin (Android Market)