Exchange/W2K3 Licensing

When I install windows server 2003 standard x64, i’m going to install an additional 40 CALs for a total of 45 cals. when i install exchange 2007 std on that server, do i need to install additional CALs for exchange?

i’m upgrading from SBS2003, where the exchange mailboxes were integrated into the profile of each user, and only needed 1 CAL per user. but with win std and exch std it seems that i need 2 CALs per user, 1 for AD and 1 for exchange? is this correct?