CSipSimple for Android
From GNU Telephony
CSipSimple for Android supports audio and chat using the open and vendor-independent standard SIP for communication.
The following are some screenshots to show you two people calling each other using the CSipSimple app for Android as their software client. Both users are on the same internal Wi-Fi network, and both are using GNU SIP Witch as their service to find each other.
An account - "David hjemme" or "David home" is already added. The green bar and the word "Registered" shows the device is connected to the GNU SIP Witch service. To add an account, use the button "+ Add account".
The settings for the account named "David hjemme" or "David home" - an account name you choose, the user name to login, the IP address or domain name of the server where the GNU SIP Witch service is running, and finally the password to login.
Accepting or declining a call
Oh, look! Haakon is calling! He is also registered to the GNU SIP Witch service, but is using an HTC Desire phone with CSipSimple. To accept the call, David needs to slide the green button. To decline the call, David can use the red button.
CSipSimple is stable and easy to use. There are many other apps that support video, audio and chat using the open and vendor-independent standard SIP for communication. Remember, using an open and vendor-independent standard means you can use those apps that work best for you.