The following is the result of a discussion on Twitter started by @twkisner

The question was how to build a url that allows you to start a multiparty IM.

RT @twkisner: @paulnearney @UCMadeEasy Thank you!!! This works in #Lync "im:<sip:user1@here.com><sip:user2@here.com>"

 

A similar dialog was held internally and included 2 requests which are not possible but figured I would share as I suspect some would ask.

1. Launch a group chat channel via url.

While it is possible to provide a channel shortcut inside of Group Chat, and while you can create a url that would launch the Group Chat Client, it will not join a specific room. I used this article Registering an Application to a URL Protocol

Here is the exported regkey info

[HKEY_CLASSES_ROOT\ma-chan]
"URL Protocol"=""
@="\"URL:Group Chat\""

[HKEY_CLASSES_ROOT\ma-chan\DefaultIcon]
@="\"GroupChatConsole.exe,1\""

[HKEY_CLASSES_ROOT\ma-chan\shell]

[HKEY_CLASSES_ROOT\ma-chan\shell\open]

[HKEY_CLASSES_ROOT\ma-chan\shell\open\command]
@="\"C:\\Program Files (x86)\\Microsoft Lync Server 2010\\Group Chat Client\\GroupChatConsole.exe\" \"%1\""

2.  Launch an IM to a group

This is not possible because distribution groups and security groups while possibly email enabled, do not have a SIP-URI

Tom LCSKid