Your bill is in a band that moves up and down every month depending on your usage. Not as cheap as estimating correctly, but not as bad as paying huge overcharges if you mis-estimate.

I don't know how well it works in practice.

But since you don't like Sprint, I guess that's out.

Maybe Virgin or some other relative newcomer has a plan that would fit better?

Until then, you might want to hit *2 (or whatever magic key sequence they have that tells you how many minutes you've used) frequently. :-(

Luck!

Cheers,
Scott.
(A Sprint customer with an ancient 300 minutes/$30 a month plan that he only rarely exceeds.)