You can do both.
You can purchase your data plan up to 30 days before your travel plans. If you buy before you travel, the validity period of your data plan won't start until you first use data in your destination country.
Alternatively, you can buy your data plan when you arrive in your destination. If you don't have a Wi-Fi connection in that location, you can use cellular data without buying a plan to connect to our "captive portal", using our app or website "captive.gigsky.com", and then buy a plan.