Here's what the worst Windows 10 phones will have for tech specs
According to Microsoft's developer website, Windows 10 Mobile will require at least a Qualcomm Snapdragon 208 processor, 512MB of RAM, 4GB of storage, and a VGA (640-by-480) resolution rear-facing camera. Microsoft won't be requiring a front-facing camera, Bluetooth, or accelerometer.
The display must have a minimum resolution of 800-by-480. Oddly enough, there's no lower limit on screen size, though Microsoft says a 3.5-inch or larger screen is necessary to run existing apps built for Windows Phone 8. Stranger still, Microsoft lists "touch, touch pad, and digital pen" as optional components in Windows 10 Mobile, though we're guessing a rebirth of the trackball isn't happening anytime soon.
As Neowin notes, the baseline specs are actually lower than they were for Windows Phone 8.1, which required Bluetooth, an accelerometer, and at least a 2-megapixel camera.
Why this matters: Compared to Windows Phone 8, we'll probably won't see as many Windows 10 Mobile handsets at the very bottom of the price spectrum. Microsoft has said it wants to produce fewer phones overall, while focusing a bit more more on flagship phones and business customers. Still, it's likely that at least one phone will scrape the bottom of the spec barrel whenever Windows 10 Mobile launches.