Yes, that sounds about right. You have a mobile number associated with your account, and your bank texts you when you make a purchase. I don't think it would be required that you confirm every purchase - it would be more of a notification system. You could require it, but there's a balance of convenience and security that people are already used to.

As for not being able to purchase without a signal, I posit that in the case where you need to authorize purchases, it has the same limitations as your credit-card-communication concept :)