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 works under Linux and Windows X