SIP

The Session Initiation Protocol, the current underpinning of standard VoIP.

• RFC:3261 (obsoletes RFC:2543), RFC:3263
• RFC:3428 - Session Initiation Protocol (SIP) Extension for Instant Messaging
• RFC:3264, RFC:2327 - Session Description Protocol
• RFC:2916 - ENUM (a DNS to standard phone numbering - E.164 - mapping)
• draft-ietf-simple-presence
• draft-ietf-impp-cpim-pidf
• SIP Servlet API Spec

• Tapioca, a SIP/H.323 client library written in C.
• Vovida - reSIProcate stack.
• SIPp Performance Tester
• Shtoom (Client and Python tools)
• oSIP (libosip2)
• SIP Open Stack - Java

• Mini-SIP-Proxy - a Perl POE daemon.
• Siproxd (proxy, 2004)
• partysip (proxy, 2002 but allows local registration)
• SaRP - SIP and RTP proxy in Perl

Clients (more)

• Java Presence Proxy

• YATE
• Asterisk (general purpose PABX) GUI Client
• NIST JAIN SIP Reference Implementation
• sipX

• playSIP - a session recorder.
• callflow - a set of tools that use Batik to generate SIP call flow diagrams
• SIPp - a free load generation tool

• Getting the Dial Pad in Windows Messenger:

Set the following DWORD Registry key to 1:

In 4.7:
HKEY_CURRENT_USER\Software\Microsoft\MessengerService\CorpPC2PHone
In 5.1:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Messenger\Client\CorpPC2PHone

• Certificate Generator for Sipura hardware (lets you encrypt the data stream between devices without resorting to traditional VPN techniques)
• SIP Servlets Overview
• SIPfoundry - hosts a few projects
• SIP Drafts: APIs and Programming Environments - includes mention of a PHP SIP environment.
• VoIP-Info (VoIP-oriented wiki)
• Slashdot: Cheap and Reliable IP Telephony? - discussion and a few more links.