If a prisoner works a day $3.50 and calls cost $0.25/min, then a prisonor can afford a 14 min call for a day’s labor. Yes, these numbers are quite realistic.
Supply maintenance is near zero. Demand is elastic but there’s no alternatives. Max profit is obviously not at the highest prices.
Helping prisoners was never the goal. It’s convenient optics, icing on the cake of profit maximization.
Did you know that the US never abolished effective slavery. It’s perfectly legal for prisoners. Always has been. It’s even in the federal Constitution.