Windows Server 2003 R2 Device Client Access License with Software Assurance. A CAL provides the right to access a specific program. You need a Device CAL for every user that wants to access that program. A minimum of 5 CALs is required as well as a server license. This CAL license includes Microsoft's maintenance program Software Assurance.For licensing questions contact our Microsoft Certified Professionals at 1-800-474-1045 ext 3.