Yes, T-Mobile is giving them away for free, though of course there are caveats. The deal requires an eligible trade-in with T-Mobile's JUMP! On Demand program. You'll also have to pay "taxes and fees," and if everything checks out, you're good to go.
You'll need a relatively new device to trade-in to T-Mobile to qualify for this deal. Phones that qualify include the iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, Galaxy S6 Edge, Galaxy S6 Edge+, Galaxy S5, Galaxy Note 5, Galaxy Note 4, and Galaxy Note Edge. T-Mobile also lists the Galaxy S6 as being an eligible phone to trade, though why anyone would want to trade one phone for the exact same model is something that escapes us.
The Galaxy S6 is Samsung's flagship smartphone. It sports a 5.1-inch Super AMOLED display with a 2560x1440 resolution, 64-bit octa-core Exynos 6420 processor, 3GB of RAM, 5MP front camera, 16MP rear camera, 802.11ac Wi-Fi, Bluetooth 4.1, NFC, 2,550 mAh battery, and various other bits.
In addition to the free phone and tablet, T-Mobile for a limited time is offering 10GB of 4G LTE data for each line in your family for $30 per line. If that's not enough, you can double the data to 20GB for an additional $10 per line.