Have you thought about offering pay monthly plans with zone data instead of national data? I find 100mb on my current plan goes through rather quickly.
eg. instead of having 100mb national data, i would prefer to have 250mb of broadband zone data.
Alternatively it would be great if I could buy broadband zone data in either smaller chunks or longer validity periods. Currently the cheapest option if 100mb is not enough for you is to pay an extra $20/month for 1GB. (The other broadband zone options work out at $25 / month ($50/2 or $150/6)
Any of the below packs would be good
100mb / 1 month for $5
300mb / 1 month for $10
500 mb / 2 months for $20
1GB / 3 months for $25