Linphone through GNU SIP Witch on Debian
From GNU Telephony
This is my desktop on my ASUS Eee 1005HA. I run Debian GNU/Linux 6.x Squeeze with the KDE 4 Plasma Netbook desktop environment. In the top right corner you can see the Linphone application start icon. Linphone supports audio, video and chat using the open and vendor-independent standard SIP for communication. If you look closely, you can see a smaller version in the top bar - that's because I've already started Linphone.
Here I am, using the built-in web-cam on my netbook. In the top right corner, you can see a chat window with messages sent through my Wi-Fi network from my HTC Desire phone, where I also have a SIP client - that one is called CSipSimple. Remember, using an open and vendor-independent standard means you can use the apps that works best for you.
GNU SIP Witch makes it possible for both clients to find each other, so you can talk, use video or chat. See screenshots of CSipSimple for Android receiving a call using GNU SIP Witch as a service.