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:firstname.lastname@example.org><sip:email@example.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
@="\"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