Microsoft has issued a statement on the ChevronWP7 unlock tool for Windows Phone 7, that allows owners to trick the OS into registering itself as a WinP7 developer device with the app rather than Microsoft directly. Microsoft normally charges $99 a year for the privilege of loading developer apps.
We anticipated that people would attempt to unlock the phones and explore the underlying os. We encourage people to use their WP as supplied by the manufacturer to ensure the best possible user experience. Attempting to unlock a device could "void the warranty, disable phone functionality, interrupt access to WP7 services or render the phone permanently unusable." (emphassis added)
Long Zheng replied and asserted his position on the tool he helped create,
[…]The sole purpose of the tool is also quite simple -- to enable anyone to sideload an unpublished app to their WP7 device. I must emphasize the ability to sideload and run unpublished apps is a supported functionality of all WP7 devices. Although not enabled by default, it's a behavior embedded into the design of the operating system itself. That's all ChevronWP7 does[…]
Rafael Rivera has posted that the Microsoft statement came from the company's UK branch and doesn't represent an official Microsoft view.