If you want to mess with your WP7 phone but don’t want to pay the $99 yearly fee to be a developer, ChevronWP7 has released the tool for you! For a paltry $9, you get what is essentially a hobbyist account. You can grab code from others (or write your own) and run and debug it on your own phone. XAP files are widely available on forums such as XDA-developers, and now you can easily grab them and put them on your phone.
It’s simple; Log in with your Live.com account, pay for an unlock token and use that token with the special unlock tool to unlock your device. Then grab the WP7 Dev Tools and be on your way! Now, you can’t publish any apps to the marketplace, you’ll need a full developer account, and they recommend you deactivate your Chevron account to keep it from getting hairy.