The $60 plan, for example, now offers 5GB, when it was 1GB previously. You now get 1GB for $40, and the 300MB for $20, though you do need to use the data within 30 days. As before, there's a $10 plan that only gives you 100MB that you need to use in 10 days instead.
There are no activation fees, and megabytes can be added as needed. To use it, you can buy Virgin Mobile's Novatel EV-DO Rev. A modem for $99.99.