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