Not if you want approval from the payment card industry you can't.
They'll want proof that no other app can access the screen, that screen presses can't be recorded and lots of other stuff.
I'm going through this with a hardware pinpad at the moment, the list of requirements is very long and quite stringent.
--edit-- I'm not saying this is impossible, but I find it very unlikely. All the other EMV devices I know of that are designed for use with iOS and Android devices have built-in hardware pinpads because it's just easier... the PCI is very precious about PIN data. For good reason.
