Linphone is an internet phone or Voice Over IP phone (VoIP).

• With linphone you can communicate freely with people over the internet, with voice, video, and text instant messaging.
• Linphone complies to the SIP protocol, an open standart for internet telephony. Linphone should be able to interoperate with most SIP-compatible phones and proxies.
• If you subscribe a VoIP to PSTN (=classic telephony) account to a telecom provider, you can reach everyone that has a "classic" phone line. However those calls are not free since PSTN networks are costly.
• linphone is free-software (or open-source), you can download and redistribute it freely.
• linphone is stable under Linux, but FreeBSD and OpenBSD are reported to work.
• the windows port is stable but some features are missing as the graphical interface is incomplete and under heavy development.