There's also a technical hurdle of the telco can't know where you're coming from over the Internet. The terminate your end of the vowifi call and from there they only charge for the connection as though it originated in their network, which is all they know for sure (that is their SIM and your account that's authenticated from somewhere in the world)
Well, I know at least one provider that looks at your IP's country registration and will block you if they believe it's not domestic: Vodafone Germany. I wouldn't wish their service upon my worst enemies.
