$20 - 1GB - 30 days (10c/MB if overlimit)
$50 - 3GB - 60 days (10c/MB if overlimit)
If you purchase the 1GB plan monthly for 2 months and then use an extra 1GB it is the same price as the 3GB pack, however if you use less than 3GB you save money.
What is the point of the 3GB data pack it should give better value for spending more $$.
Can I suggest 3GB should be 90 days (I actually thought it was 90 days when I purchased it, I think maybe it used to be 90 days or there used to be some kinda special?)