One thing I always wonder: your typical cell plan (that I'm familiar with) with, say, 6 GB per month would be completely used up within, what, 5 minutes or less

One thing I always wonder: your typical cell plan (that I'm familiar with) with, say, 6 GB per month would be completely used up within, what, 5 minutes or less? And then you can either pay more or wait for next month? What's the point? (Yes, and presumably they'll increase the cap, but even a 100x increase would give you 1 full day of usage per month.)