Dear Alessandro,
SQL Server 2005 has three kinds of licenses: Per processor, per device and
per user.
You can refer to:
SQL Server 2005 Licensing
http://www.microsoft.com/sql/howtobuy/default.mspx

However I'm not sure of the meaning of call license you mentioned.

Since the question is a license issue, you can call 1-800-426-9400, Monday
through Friday, 6:00 A.M. to 6:00 P.M. (Pacific Time) to speak directly to
a Microsoft licensing specialist, and you can get more detail information
from there. Worldwide customers can use the Guide to Worldwide Microsoft
Licensing Sites to find contact information in their locations.

Sincerely,
Charles Wang
Microsoft Online Community Support

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