Have you tried applying for jobs lately? Ok, so you can use the internet at a library. But you can't afford a car, so now you need to take the bus across town, with your the kids in tow...
I would not want to apply to anything via a smart phone. While you may get away with 3g and a hotspot for getting through critical online activities like job applications, my experience has been that mobile carriers will charge for the ability to hotspot if they can. Not a solid option for the poor. A better option would be something like Juno/NetZero with N hours free per month, but with speeds that can actually handle today's bloated websites.
Until you realize that the pre-paid phone service doesn't exactly work well for that and is rather expensive, and your refurbished phone doesn't work too well with modern websites.
I should also mention that not everywhere has access to a public library that is free to use. I lived next to one of those districts - the next township (and town) over didn't have one. Since they didn't pay taxes into the library, they had to pay a yearly fee. Only pre-school children were exempt.