When you register as a developer on App Hub you have an year fee of $99. This will allow you, last time I checked, to unlock up to 3 phones so you can deploy your apps and to submit your apps to the market for publishing.
Last year a few guys released a tool with the name CheveronWp7. This tool would allow you to unlock your phone so you could deploy apps to it for free, without having the need to have a developer account.
Microsoft acted fast on these guys and asked them to remove the tool and made an interesting move. It has adopted the tool and collaborated with them to release it to the public in an official way.
So now, this tool is available for $9 and its an official supported tool. Its seems o be aimed at the hobbyist developer that wants to do some apps and deploy to their own phone and for developers starting to develop apps, that dont want to register just yet on the App Hub until they submit the first app.
This tools does not allow you to publish apps to market and you cant have more than 10 apps deployed to the phone "off-market". As far as I know you can only unlock one phone and you need to have a paypal account. Still for the price is a much better alternative than hacking your phone as I saw some do recently on other foruns, voiding the warranty and creating all sort of other problems.
For me this is a good opportunity to spread word and have more devs to start to play with Windows Phone. $9 is 10x less than $99 and for some while this is not a huge amount, to others it may be the difference of giving a go at building apps or not.
I still recommend that devs register on App Hub because not only you can unlock more phones but there is also the advantage of publishing and thats what we are all aiming to right?
For anyone interested, you can find the official tool here: http://labs.chevronwp7.com/