Your phone doesn't have to come from your carrier.
You can buy a Galaxy S9 or S9+ just about anywhere, and in the U.S. most people will typically buy directly from their current carrier or one they're in the process of switching to. But you don't have to buy from a carrier — you can buy a GS9 or S9+ unlocked, and even have a choice of multiple retailers from which to get it.
The U.S. unlocked Galaxy S9 is designed to work on all major carriers, including Verizon and Sprint, and in terms of hardware it's identical to what you'd get from those carriers. There are differences in software, too, but for the better — you don't have carrier customizations or pre-loaded apps to contend with. There are also zero hoops to jump through if you ever want to switch carriers — being unlocked from the get-go, you can just switch SIMs and be on your way.
You really should consider buying your Galaxy S9 or S9+ unlocked — and when you do here are the places you can buy one, and the reasons why you'd choose each retailer.
When buying unlocked from Amazon, it's important to be sure that you're buying the proper model. Amazon does sell proper unlocked Galaxy S9 and S9+ models with full U.S. carrier compatibility and warranties, but third-party sellers also offer international models — ones that may not have complete carrier compatibility and definitely don't have a U.S. warranty. We've linked to the proper model below.
Amazon offers 12-month no-interest financing for purchases of $599 or more using its self-branded credit card. This isn't as generous as what Samsung or carriers may offer, but it does help you spread out the cost of these expensive phones when buying unlocked.
Best Buy has the Galaxy S9 and S9+ available unlocked right next to the carrier versions. In many cases, the unlocked models will be listed for less than the carrier ones as well, though you won't see all of the purchase incentives the carriers offer. There aren't any concerns over getting the right model — Best Buy only sells the U.S. unlocked version of the phones.
You can also get 12-month no-interest financing from Best Buy on your Galaxy S9 or S9+ purchase using its store credit card.
If you're going to buy a Galaxy S9 or S9+ unlocked, Samsung is the simplest way to go — though it may not always be the cheapest. There's a better chance you'll find a discount on Amazon or Best Buy, but there's never anything wrong with buying direct from the manufacturer on Samsung's website.
One huge benefit of buying from Samsung directly is that you can get your Galaxy S9 or S9+ with more internal storage. For an extra $50 your can move to 128GB of storage, or for $120 you can get 256GB of storage. This is only available from Samsung's online store, so if you need more storage, this is your only choice.
You can also get 24-month no-interest financing for Galaxy phone purchases, which is on par with the terms that carriers offer.