The OnePlus 7T has been discounted to $399.99 several times in the past couple of months, and the same deal is back again if you missed out on it previously. The 7T may no longer be the newest OnePlus phone, but it offers a ton of bang for the buck at this price point.
With a Snapdragon 855+ and 8GB of RAM, this is no slouch in the performance department. Other specs include a 6.6" 1080p AMOLED display capable of 90Hz, 128GB of storage, a triple rear camera setup (48MP primary + 16MP wide-angle + 12MP telephoto), and a 16MP selfie-shooter.
Woot says that this is the HD1907 model, meaning that it's an unlocked T-Mobile variant that will work on all GSM carriers. The biggest downside of this is that Verizon isn't supported. Updates are slower, but you can flash the regular OxygenOS software if that bothers you. It also doesn't have dual-SIM support natively, but all you need is a dual-SIM tray, which can be purchased inexpensively on eBay.
Shipping is free for Amazon Prime members, and both the Glacier Blue and Frosted Silver colors are available. Remember, this deal is for today only (13 hours remaining as of publishing time), so act quickly.