I received an email via the blogs from Arun this week about the options he has to connect to LCS while running a UNIX/Linux OS.
The Microsoft solution is Communicator Web Access, but this is a server install enabling browser support for clients. Like many of us Arun is not that admin so this is not an option.
3rd party clients is the only other way to go -
Trillian and Gaim are the two options I am aware of, and from an earlier post you can see that I use Trillian personally due to my support for Public Internet Connectivity (PIC) which requires me to be able to test AOL, MSN, Yahoo! accounts with customers. Trillian also offers a SIP plug-in for which I have used successfully while internal to our corporate network (it does not work when I am home via the Access Proxy for some reason). Trillian is also a Windows only client so this won't be an option for any of the UNIX/Linux users.
Gaim offers a Windows and Open Source solution and I have tried both. I am not by any means someone you should think knows anything on Linux but I use the Ubuntu distro for my testing in a Virtual Machine. Our investigation on this issue appears to show that the way Gaim combines the server and alias information assumes information about the server deployment. What Arun and I have found in our testing shows that the client queries for the server but the server based on the alias won't work with a typical LCS deployment.
For example my alias is toml (at) microsoft (dot) com so there is a DNS SRV query for microsoft.com but our servers for lcs are host.microsoft.com so there will not be a valid connection.
What I said to Arun is that I believe the Gaim client was not likely written for the LCS product but for the other SIP products (open source) available. Thus we are at a stand still and if you have any info or thoughts let me know. Remember I am NOT a developer :)