How would you refactor this?

`ExpensiveQuery` must only run when necessary.

```
DECLARE @city VARCHAR(10)
DECLARE @status INT

IF @status = 5
BEGIN
    SELECT c.Name, c.Phone
    FROM Customers c
    WHERE c.City = @city
    AND c.Status = 5
END
ELSE IF @status = 10
BEGIN
    SELECT c.Name, c.Phone
    FROM Customers c
    WHERE c.City = @city
    AND c.Status = 10
    AND c.SignUpDate NOT IN (EXEC ExpensiveQuery)
END

```