Update: Shortly after I posted this article, Peter Henry noted that he had a very similar article out already. Here is the link to it – it has good additional information – check it out: http://www.pchenry.com/Home/tabid/36/EntryID/389/Default.aspx
So you got your Windows Phone 7 device, you downloaded the free development tools and now you are itching to write your first “Hello World” app for WP7. You fire up VS 2010, create a quick phone app, connect your WP7 device to your development PC, select “Windows Phone 7 Device” as a target and attempt running your first app on your phone.
You will get the following message…
You have to make sure your device is ”developer unlocked” before you can deploy applications to it. Here’s how you unlock your device:
Easy! (not necessarily straightforward though :) )