Provided you have PlayStation Plus or Xbox Live Gold
So far, the Destiny beta's been gated off from the public-at-large. Well, sort of. A pre-order would grant you access, and registering your code would get you even more codes, so it wasn't too difficult to find a way in. As of right now, that barrier's completely removed for everyone.
In a post on Bungie's site, the developer announces that as of this moment (July 24 at 4:00 pm PDT), the Destiny beta is completely open, provided that you have a console that's equipped with PlayStation Plus or Xbox Live Gold. According to Bungie, there should be ads popping up on the consoles later today prompting the download. If you haven't jumped in yet, give it a spin. Walk a mile in a Guardian's shoes until the whole spectacle shuts down on July 27 at 11:59 pm PDT.
Destiny Beta: All Access [Bungie]