Linphone is a web phone: it let you phone to your friends anywhere in the whole world, freely, simply by using the internet. The cost of the phone call is the cost that you spend connected to the internet. Here are the main features of linphone: Works with the Gnome Desktop under linux, (maybe some others Unixes, but this has never been tested). Nevertheless you can use linphone under KDE, of course ! Since version 0.9.0, linphone can be compiled and used without gnome, in console mode, by using the program called “linphonec” Works as simply as a cellular phone. Two buttons, no more. Linphones includes a large variety of codecs (G711-ulaw, G711-alaw, LPC10-15, GSM, and SPEEX). Thanks to the Speex codec it is able to provide high quality talks even with slow internet connections, like 28k modems. Understands the SIP protocol. SIP is a standardised protocol from the IETF (http://www.ietf.org), that is the organisation that made most of the protocols used in the internet. This guaranties compatibility with most SIP – compatible web phones. You just require a soundcard to use linphone. Other technical functionnalities include DTMF (dial tones) support though RFC2833 and ENUM support (to use SIP numbers instead of SIP addresses). Linphone is free software, released under the General Public Licence. Linphone is documented: there is a complete user manual readable from the application that explains you all you need to know. Linphone includes a sip test server called “sipomatic” that automatically answers to calls by playing a pre-recorded message. How to use linphone ? To call somebody, you must provide to linphone a SIP URL: It is something like [email protected], where toto is a linux user that runs linphone, and machine.com is the name of a host on a network. If you don’t know the machine’s name you can specify simply an IP address in dot notation (as 192.0.0.1) If you want more information about linphone, read first the user manual. For documentation on the internals of linphone, see section « developers » of this web site. Compatibility: Linphone is mostly sip compliant. It works successfully with these implementations: eStara softphone (commercial software for windows) Pingtel phones (with DNS enabled and VLAN QOS support disabled). Hotsip, a free of charge phone for Windows. Vocal, an open source SIP stack from Vovida that includes a SIP proxy that works with linphone since version 0.7.1. Siproxd is a free sip proxy being developped by Thomas Ries because he would like to have linphone working behind his firewall. Siproxd is simple to setup and works perfectly with linphone. Partysip aims at being a generic and fully functionnal SIP proxy. Visit the web page for more details on its functionalities. Linphone may work also with other sip phones, but this has not been tested yet. So if you want to complete the list by testing with your own sip phone, contact me. Linphone uses the SIP protocol to establish calls, for that reason it cannot work with H323 phones, because SIP and H323 are different and opposite protocols. H323 phones are Netmeeting (for windows), Gnome-meeting (Unix), OpenPhone…