Note: SQL Server 2008 Pricing and Licensing by Microsoft
SQL Server licensing and pricing are to intervined subjects and very important. I strongly suggest to use properly licensed SQL Server in any production environment. The concept of licensing can be confusing sometime to new administrators. If there is any confusion one should read following documentation from Microsoft for the purpose of clear idea and understanding.
SQL Server 2008 is available under three licensing models:
Server plus device client access license (CAL). Requires a license for the computer running the Microsoft server product, as well as CALs for each client device.
Server plus user client access license (CAL). Requires a license for the computer running the Microsoft server product, as well as CALs for each user.
Processor license. Requires a single license for each CPU in the operating system environment running SQL Server. This license includes unlimited client device access.
Following document explains key licensing considerations for SQL Server 2008 customers.
Abstract courtesy : Microsoft
Reference : Pinal Dave (http://blog.SQLAuthority.com)