The Portable Freeware Collection ⋆ FGR* Blog
MicroSIP allows high quality VoIP calls via the open Session Initiation Protocol to other SIP-compatible phones or regular telephones. The program is easy to configure and light on system resources and supports video, instant messaging, secure connections (via client-to-client TLS encryption) and standards compatibility.
This SIP softphone is based on the Windows PJSIP stack. For regular phones, the program requires an account with a (non-free) SIP Provider.