This service as 'billed' is not worth $30+ a month... (once they throttle and your subscriber experience hits the toilet). If you can't offer at least 1 megabit throttled instead of 256kb you might as well pack it in and stop offering service now. Who cares if it's even so-called unlimited if the bandwidth is barely enough to carry VOIP, let alone other kinds of data.
I use 200-600MB / month, so this limit is far beyond what I use. Also, I never see speeds beyond ~500kbps anyway on Sprint, so throttling to 256kbps wouldn't be earth-shattering.