| 3CX: Developers of IP PBX software for Windows. |
| Applied Voice & Speech Technologies, Inc. (AVST): Applied Voice & Speech Technologies, Inc. (AVST) offers SIP integrations to its flagship CallXpress unified communications platform |
| BaseVoice: Commercial software development company that produces PBX, router, proxy and application server software. |
| Bluenote Internet Telephony Networks: Server software targetted at the enterprise sector. |
| Interactive Intelligence, Inc.: Developers of a proxy server. Site contains downloads, documentation and a forum. |
| LignUp Corp: Applications developer. Products include software PBX's for enterprise and service providers. |
| OpenSER: A branch of the SIP Express Router project, offering an open-source SIP server. |
Classical
