T-Mobile's Galaxy S9 and Galaxy S9 Plus pre-orders are already arriving for some customers who placed the orders as early as possible. This shouldn't be too much of a surprise as this typically happens from most major carriers, and last year is a good example as pre-order units showed up earlier than launch dates for T-Mobile and other carriers back in 2017. Though not all consumers who pre-ordered a device will have already received the phones, it is reported that some users are seeing these show up at their door as of today, which means the pre-orders will likely continue to arrive early over the next couple of days leading up to the launch on Friday.
So far it only seems like T-Mobile has started shipping out phones early, but there is every chance between now and Friday that other carriers such as Sprint, AT&T, and Verizon will start shipping the pre-order phones out early to consumers who bought the phones as well. All that said anyone who hasn't received their Galaxy S9 or Galaxy S9 Plus pre-order by now won't have to wait too much longer in the event that it doesn't come early considering the official launch is in a few days, and that's likely when most pre-orders are going to begin arriving for the majority of people.
While there are some benefits to wait for the phone to officially launch before you buy a new device, like being able to walk into a retail store and physically play with it before you decide to make the purchase, there are benefits to ordering early as well. Nearly every year Samsung as well as the carriers end up offering pre-order bonuses, so there's usually an incentive for consumers to place pre-orders as it could help them earn a couple of freebies. Samsung's Galaxy S9 and Galaxy S9 Plus will be available through Samsung and Amazon as well as other online retailers unlocked for $720 and $840 respectively for the 64GB models, and at the carriers pricing will be specific to each carrier, so if you're able you might be better off buying the unlocked models as they will be the least expensive.