In India, the following lower caste laborers have been doing business with their mobile phones for at least a decade:
* Laundry/Dry cleaners
* Drivers
* Grocery Delivery
* Home cleaning
These folks have been doing the same work for a long time, and as cell phones got cheap in India they just started using them. Their standard of living may have gotten better, but their social standing really has not.
In my occasional travels to SF, I am starting to see a similar caste system emerge. And it's pretty depressing.