Openfire 3.5.2 and Spark 2.5.8

Openfire (formerly Wildfire) is a cross-platform real-time collaboration server based on the XMPP (Jabber) protocol.
You can check here this Opensource solution.
Using Spark 2.5.8 with Phone plugin is excellent for IM solution and asterisk VoIP integration.

Migrating Windows Small Business Server 2003 to New Hardware

If you decide that your server running the Windows® Small Business Server 2003 (SBS) server software is no longer able to keep up with the demands of your organization, and expansion is not a viable option, you can use this guide to help you migrate the Windows SBS 2003 settings and data to new hardware.
Click here