The Prototype iPhones That Hackers Use to Research Apple’s Most Sensitive Code - Motherboard

https://motherboard.vice.com/en_us/article/gyakgw/the-prototype-dev-fused-iphones-that-hackers-use-to-research-apple-zero-days

Very few people have heard of them, but “dev-fused” iPhones sold on the grey market are one of the most important tools for the best iOS hackers in the world.