Unified Communications by Yann Espanet

Use this tool from Microsoft to compare the cost of your own infrastructure with the cost of hosted services with the same number of users :

http://www.microsoft.com/online/estimator/default.aspx

Here is a sample list of prices with this tools  :

 It cost only 2,5 $ per month and per user for Office Communications Online !

Related posts:

1. Microsoft Office Communications Online : Software Plus Services (S+S) mode for UC
2. UC Microsoft-hosted services : Business Productivity Online Suite (BPOS)
3. TechNet Webcast: Enabling External User Access in Communications Server 2007 (Level 200)