The same limitation appeared recently on the play store (so it's still possible to do in Android if I would publish in alternative store). The monetization is simple: every SMS is sent by your device so the pricing is the pricing of your network provider. Also if you want to send messages to more than 10 contacts you need to unlock the premium textblast through an in app purchase. So yes your contact list is safe. I doesn't work with Google Voice looks like it's only US based and I am in Europe.