At T-Mobile, buy one Samsung Galaxy S8 4G LTE Android Smartphone for T-Mobile in three colors (Black pictured) bundled with a SIM Starter Kit for $55 up front plus $30 per month for 24 months with a qualifying plan and finance agreement, and get a second one for free. (Alternatively, you can opt to pay the total price of $750 up front.) Even better, free shipping applies. It features an octacore (2.3GHz Quad + 1.7GHz Quad) processor, 5.8" 2960x1440 touchscreen Super AMOLED LCD, 4GB RAM, 64GB internal storage, dual 12-megapixel rear-facing cameras, 8-megapixel front-facing camera, 4K video recording at 30fps, 802.11ac wireless, Bluetooth 5.0, microSD card slot, water-resistance, and Android 7.0 (Nougat).
Also at T-Mobile, buy one Samsung Galaxy S8+ 4G LTE Android Smartphone for T-Mobile in three colors bundled with a SIM Starter Kit for $155 up front plus $30 per month for 24 months with a qualifying plan and finance agreement, and get a second one for free. (You can opt to pay the full amount of $850 up front.) It features the same specs except it has a 6.2" screen.
Note: For a limited time, with the purchase of either phone above, you can also get six months of Netflix, a Clear View standing cover, and a 64GB EVO+ memory card. See details here and here.