Go with Microsoft LCS if you have an Exchange/Outlook environment and want to easily extend it into the world of IM.

There are other smaller vendors that are entering the IM market. One to watch is Antepo Inc., which offers a system called Rivoli. They differentiate themselves by supporting a wide collection of public and private IM systems using a collection of SIP-based gateways to federate among Microsoft LCS, Lotus Sametime, Extensible Messaging and Presence Protocol servers and even AIM. Rivoli costs $36 per user, plus a maintenance fee after the first year. It can work with older Microsoft Exchange clients as well as integrate quite nicely into Sharepoint, Microsoft Messenger and other Windows products as well as Apple Computer Inc.'s iChat.

"We were seeing people wanting enterprise-grade Skype with the benefit of standards and a secure infrastructure, said John Sullivan, a product manager at Antepo. Rivoli Version 7.0 is shipping by the end of the summer.

Jabber and open sources

Finally, there are the open-source alternatives that involve implementations around the Jabber server and people running its protocols, called Extensible Messaging and Presence Protocol, or XMPP. Last year, support reached a new milestone with Google Talk and the Gizmo Project using these protocols.