Welcome to the forums.

When was the last time you have populated the indexes on the table/database?

Thank you for answer.

It was when I filled the table with data... I've also tried to delete and rebuild the full text catalog, but without improvements.

The DB is composed by only one table, and the query string is saved into a stored procedure.

This is the query string:

SELECT * FROM Annuario
WHERE(
            (
            (Cap = @CAP)
            AND
            (
                    (
                    CONTAINS(Telefono,@TEL) OR
                    CONTAINS(Fax,@FAX) OR
                    CONTAINS(Mail,@EMAIL)
                    )
            OR
                    (
                    CONTAINS(RagioneSociale,@RAGSOC) OR
                    CONTAINS(Nome,@RAGSOC)
                    )
            AND
                    (
                    CONTAINS(Indirizzo,@INDI) OR
                    CONTAINS(Citta,@LOC)
                    )
           
            )
            )
            OR
            (
                (
                CONTAINS(RagioneSociale,@RAGSOC) OR
                CONTAINS(Nome,@RAGSOC)
                )
                AND
                (
                CONTAINS(Telefono,@TEL) OR
                CONTAINS(Fax,@FAX) OR
                CONTAINS(Mail,@EMAIL)
                )
            )
            OR
            (
            CONTAINS(Indirizzo,@INDI) AND
            CONTAINS(Citta,@LOC)
            )
           
        )

What kind of difference in configuration of development & production environment?

As you say Development is 2005 and Production is 2008, which is something I see as a show stopper in performance in terms of system configuration on hardware.

Also in the query try to count only one field and do not use *. Try to use the SQL below where field_id is an index in your table. Use change tracking with the "update index in background" option & limit activity when population is running.