In the event your Galaxy S7 pre-order has been delayed, you can just cancel that sucker. As with the S7 Edge, the regular Galaxy S7 has appeared on eBay in its unlocked form. For $599.99, you can get the SM-G930F with support for most GSM/LTE networks. That's about $100 cheaper than the full price GS7 on US carriers.
Importantly, this is an international phone. That means it has an Exynos 8 SoC instead of the Snapdragon 820 in US models. The LTE bands should be great, though. It even has band 12 for T-Mobile. 3G is missing Tmo's band 4, but you'll be fine on HSPA+ data in areas where T-Mobile runs 1900MHz.
Shipping is free in the US, and you can
choose between the black, gold, and silver versions of the device. Tax is only paid in Missouri. International shipping is available too.