The blog..

Microsoft seems to have simplified the approach to CALs a bit in 2008 which we can only be grateful for Up until now it has pretty much been a question of new CALs when upgrading your TS/XenApp environment. However that seems to have changed with 2008.

In Windows Server 2008 R2, Windows Server 2008 TS CALs and Windows Server 2008 R2 RDS CALs will be treated as equal in all respects. So, if a customer has a Windows Server 2008 TS CAL, it will allow the same functionality (connection, experience etc.) as a Windows Server 2008 R2 RDS CAL.

Quote from: RDS Blog

This goes for both installation and issuance. Windows Server 2008 TS CALs can this way be issued from a Windows Server 2008 R2 server. Besides a post on the RDS blog i do not have too much info, but i will investigate and update accordingly.

for more information on TS/RDS CAL licensing: http://www.microsoft.com/windowsserver2008/en/us/licensing-terminal.aspx

Rene Vester