2008 Server Licensing Question

Hi,

We’re planning on moving from an SBS2003 server to 2 x Windows 2008 servers.

Server A to run as PDC with File & Print sharing
Server B to run as an Exchange 2010 server

with a mixture of 50 users local and remote (we already have a 2003 TS server with appropriate CALS that will remain untouched apart from connecting to the new domain)

We obviously need 50 CALS for Server A & 50 CALS for Exchange 2010. But do we still need another 50 2k8 CALs for Server B?

Thanks in advance

Peter