You should be able to buy a SIM card when you arrive. In most airports there are kiosks that sell local SIM cards. However, the rates may be a little higher than if you bought one outside of the airport. You can always opt for the cheapest prepaid SIM at the airport and top up later on. Alternatively, some countries (like Japan) allow visitors to pre-purchase SIM cards online, which can then be delivered to their hotels. In some cases, you may be able to use your current SIM via your local service provider. Still, you'll want to check roaming rates to make sure that you're not spending a fortune. If you switched to a new SIM and are getting the "No SIM card detected" error, learn what to do.