To get a free memory card with the Galaxy S9, S9+, or Note 8, you have to buy the phone from Samsung directly…
The memory cards offered as gifts are Samsung-branded and will match the storage capacity of the Galaxy S9 or Galaxy Note 8 that you’re buying: 64 GB, 128 GB, or 256 GB. Both unlocked and carrier versions of Samsung’s high-end smartphones are included in this deal, and you can even get the brand new Sunrise Gold S9 and S9+ that Samsung released at the end of June. Your free memory card should be automatically added to your order at checkout, regardless of the payment method that you’re choosing.