I believe you can play any purchases on two devices. It used to be five, but they reduced it because people where abusing that to share games with other people. So for example, you could play on your PS3 and PSP. I think you will also be able to de-activate your PSP if you're going to get a Vita, then activate the Vita to your account and play the games on the Vita, but you would no longer be able to play them on the PSP.