Hi Emmanuel,

Cisco Unified Communications Manager Business Edition is a designed for medium-sized businesses with up to 500 employees and up to five remote sites. This would be a good fit and probably the most cost effective :)

http://www.cisco.com/en/US/products/ps7273/products_data_sheet0900aecd805e6985.html

Here is a link to a good video that describes the Cisco Unified Communications Manager Business Edition;

http://www.cisco.com/en/US/products/ps7273/index.html

Hope this helps! And best of luck,

Rob