When I say poor people, I am talking about third-world, living in slums poor people. Not college student "I only eat Ramen noodles and live in a studio apartment" poor, which really isn't poor at all if people had a grip on reality.
$50 is a monthly salary for most of the world.
Anyways, liteclients can even do without headers with the right node configuration. I don't see any reason why we can't get Bitcoin into the hands of Africans who transact with Nokias as their means of living. The solutions are feasible.
You just defined bitcoin out of the equation. Someone that lives on $50 a month doesnt have enough money for bitcoin. Who is he going to pay with it? You think the goat farmer two huts down accepts it? Its cash only at those levels by necessity.
You are trying to design a solution for a problem that doesn't really exist.
If and when bitcoin ever gets so pervasive that its used in those types of areas, it will be down on hand-me-down $10 androids. Or more likely from the "internet cafe's" computer which runs a community wallet service for a fee....Not some bitcoin over SMS on 16k micros.....