I don't presently own a Windows Phone so perhaps this is a naive question.
I was thinking about buying a Windows Phone (maybe Lumia 520 or 530) to use on Wi-Fi only, so an unlocked/no-contract phone. But then I wondered, if you have an unlocked/no-contract phone, who controls the OS updates? That led me to the answer that "Phones that are branded to a carrier are subject to the carrier's update schedule even if the phone is unlocked".
Are there any non-carrier phones?
How would a developer get OS updates to test/develop against?