42 Services for the design, development, installing, updating, maintenance of and providing computer software to enable voice calling, voice mailing, call forwarding, video calling, video conferencing, simple message service (SMS), instant messaging, screen sharing, digital file transfer between users and user presence indication, all of the aforementioned communication functions being made available to users within one software application graphical user interface and all communications arising from such functions being transmitted via the Internet or via a peer-to-peer computer network; providing on-line computer software to enable Session Initiation Protocol (SIP) communications; providing on-line computer software to enable voice over Internet protocol (VOIP) and Private Branch Exchange (PBX) communications; providing on-line computer software to enable voice over Internet protocol (VOIP) and public switch telephone network (PSTN) communications, providing on-line computer software to enable Unified Communications (UC) communications, namely, simultaneous voice calling, video calling, video conferencing, voice mailing, simple message service (SMS), instant messaging, screen sharing, digital file transfer between users and user presence indication, or at least two such communication functions simultaneously, all of the aforementioned communication functions being made available to users within one software application graphical user interface; providing online software for downloading by others that allows subscribers to utilize voice over Internet protocol (VOIP) communication services; providing online software for downloading by others that allow subscribers to utilize voice calling, voice mailing, call forwarding, video calling, video conferencing, simple message service (SMS), instant messaging, screen sharing, digital file transfer between users and user presence indication communication services, all of the aforementioned communication services being made available to users within one software application graphical user interface and all communications arising from such services being transmitted via the Internet or via a peer-to-peer computer network; services for the design, development, installing, updating, maintenance of and providing computer software to enable voice over Internet protocol (VOIP) communications via a computer network; design, development, installation, updating, maintenance of and providing computer software for use in voice over Internet protocol (VOIP) communications applications, messaging and instant messaging services, including video over Internet messaging services; design, development, installing, updating, maintenance of computer software for use in messaging and instant messaging services; design, development, installation, updating, maintenance of and providing computer software for voice calling, voice mailing, call forwarding, video calling, video conferencing, simple message service (SMS), instant messaging, screen sharing, digital file transfer between users and user presence indication, all of the aforementioned communication functions made available to users within one software application graphical user interface and all communications arising from such functions being transmitted via the Internet or via a peer-to-peer computer network