Have a plan where you charge $5 as a few and have addons like $5 for unlimited texting and $5 for a certain amount of minutes and like $15 for 500mb of data and make everyone build their own plans. I think a lot of people would be interested and offer good phones like Iphones with them.
So while I think Alex's economics might be a little unsound (i.e. $5 for unlimited texting) I think his idea is good in general. Have a lower starting point for prepaid base plans. Maybe something like 50 texts for $7.50/mo. Not everyone is texting all of the time and needing to pay for an unlimited text plan.