Only 1 PSN Account per Vita

[Jdevil3]

Euphoria14 said:

I was able to use stuff I downloaded on my PS3 Hong Kong account on my US account.

That's because even though you're logged in your US account, the Hong Kong one was still activated on the PS3. In the Vita, it obliges you to deactivate your account from the system, meaning you won't be able to play any of the content of that account if you're using another one, unlike the PS3.