The complexity arises when people want to add users to an existing enterprise contract or if they want to form a new enterprise contract that includes both software and hosted services, said Paul DeGroot, an analyst with Directions on Microsoft.

If a customer purchases a BPOS subscription for employees who will access only those services, the customer must still purchase CALs for those users, DeGroot said, even though they are not accessing the on-premise software as well.

Microsoft gives customers a discount on other parts of their license in such scenarios -- on the Software Assurance (SA) maintenance program required for enterprise agreements, for example -- but they still end up paying for something they are not using, DeGroot said. "The architecture may be hybrid but the licensing is not," he said.

Forrester analyst Chris Voce said one reason for the muddled licensing situation is that Microsoft still makes a lot of its money from on-premise software, and is hesitant to move away from that business model. "At the end of the day, Microsoft loves their recurring software relationships with their customers," he said.

Through its public relations firm, Microsoft confirmed that the number of users on contract for subscription services cannot exceed the number of CALs with SA that the customer already has.