By subscribing to a BeUnlimited mobile plan for 24 months.
The eligibility of the loyalty discount is controlled using the mobile line number, so you need a mobile plan to access it. If you have a fiber or TV subscription only, you will not have access to the discount.
If you have 3 eligible Orange lines, you can get a discount for each line. Example: you will get 3 discounts when you buy 3 smartphones over 24 months with Be Unlimited.