Make FREE pc-to-pc, pc-pc and cheap pc-to-phone, pc-phone, pc-to-fax, pc-fax, phone-to-pc, phone-pc, fax-to-pc, fax-pc, SIP-telephone, sip-to-phone calls over Internet/VoIP or ISDN/PSTN telephone networks. Use your computer as internet telephone, USB phone, USB handset, ISDN telephone, ISDN fax, answer phone, fax software, voicemail, caller ID, CLIP/CLIR, audio conferencing, call answer, call transfer, call forwarding, call waiting, call accounting, call recording, telephone exchange/PBX, etc. Works with all Firewalls, NAT and LAN routers - nothing to configure.