Can I activate more than one plan simultaneously?

No; you can only activate one plan at a time. Customers do however have the ability to change plans

E.g. You activate 7 day 1GB plan and on day 6 day change plan to the 30 day 3GB plan.

NB: If you have minutes remaining from your current 7 day 1GB plan at the time the plan was changed to 30 days 3GB, the unused minutes will then be rolled over to be used with the 30 days 3GB plan.