1. Data in your monthly plan - rollover for 2 months, hence 3 months total.
2. Data from PERK - after activation, can be used right away, expire at the end of your next billing cycle. Hence, if plan properly, PERK data can last for up to 60 days (if u activate it on Day#1 of a billing cycle).
3. Data from UPGRADE - after activation, only active at beginning of your next billing cycle. Active for 24 months. UPGRADE can be switched/changed, e.g. u r using 250MB, just received 500MB UPGRADE for Level 2, you can move the active 250MB out, then add 500MB for next month. Last only 1 billing cycle. Not sure about rollover, I read the following FAQ page few times, still not sure.