How should I understand plan days, activation deadlines and expiry?

An installation or activation deadline specifies when an action must be completed. Plan validity specifies how long service can be used after its defined starting event. Both conditions can apply and should be checked separately. A number of days is meaningful only together with its starting rule. Whether purchase, installation, activation or connection to a supported network starts the clock depends on the product and delivery instructions. After expiry or allowance exhaustion, any continuing service, additional plan options and transition rules depend on the product. A new purchase has its own order record and does not automatically extend the old plan or combine unused data. If your travel dates are uncertain, check the activation deadline before buying. Ask support about anything unclear before installing.