"Jailbreak" is a totally ambiguous term. If you want the exact level of access it provides on an iPhone - custom apps, root access, and the ability to replace system binaries - that is flat-out impossible right now. If you just want custom apps, that's actually a built-in feature of the OS.
You can try using the registry editor buit into the EM app, but most likely you're going to need to get an AppHub account.
More info on the various unlock possibilities for each Windows phone: http://forum.xda-developers.com/show....php?t=1538801
(first page of the dev&hacking section... seriously, try a *little* harder please).