So a lot of people missed this info in today's PS+ update, so I made thread just so you guys know. Also I asked community manager about it, he confirmed, that Beta is for everyone with PS+
Official PS Blog update:
Hi everyone. I hope you’ve recovered from the excitement of E3 and are ready for an epic July. Not only are we bringing you a great mix of games but there’s also the Destiny beta, which kicks off on 17th July exclusively on PlayStation. If you’re a PlayStation Plus member you will be able to fully experience Destiny and its incredible multiplayer. And if you’re not? Well, what are you waiting for, sign up now!