First tool to unlock Windows Phone 7 revealed, is called "ChevronWP7: "

A team of WP7 developers have released a tool “ChevronWP7” to unlock Windows Phone 7 devices. The developers have been working to get access into Windows Phone 7 core and they were progressing steadily. Since some time they were silent on how much progress has been made. Today, they have unleashed a simple and elegant tool to unlock Windows Phone 7.

You might be looking for a reason to unlock Windows Phone 7 device

it’ll be beneficial to indie developers who want to push beyond the limitations of the Silverlight framework and SDK – including but not limited to access to the microphone and camera. Wouldn’t it be awesome if you could override the Bing search button?

The official information regarding this tool is

Today we have an exciting breakthrough for the Windows Phone 7 homebrew community – the ability for anyone to unlock a WP7 device without a Marketplace developer account.
Unlocking allows the sideloading of experimental applications that would otherwise can’t be published to the Marketplace, such as those which access private or native APIs.
We’ve taken the pain out of the process involved and put together a super simple executable that will allow anyone to unlock any WP7 device on the market using a USB cable and just a couple clicks.
This tool is completely safe and reversible for the phone. (The app even allows you to relock the phone.)

Happy Thanksgiving with unlocked Windows Phone 7!
Download ChevronWP7
Source: istartedsomething