Wow, it seems that Sony and Microsoft are fighting each other to see who gives more gifts to the customers and this news is another example.
According to the official Playstation US Blog:
The network now expands across a wide array of digital entertainment including incredible multi-player gameplay, availability of full games day and date, streaming movies and TV shows, and a premium cloud-based music service. We are excited to provide those of you in the US and Canada with a special promotional voucher in every PS4 box* that includes:
-$10 Sony Entertainment Network wallet credit for PlayStation Store
-30-day free PlayStation Plus membership trial
-30-day free Music Unlimited service trial**
Out of the box, you can immediately experience everything PlayStation Plus for PS4 has to offer and have access to millions and millions of songs through Music Unlimited. The $10 credit can be used towards anything in the store including new PS4 launch titles, such as Assassin’s Creed IV Black Flag, Battlefield 4, Call of Duty Ghosts, and Killzone Shadow Fall.