Here are a few different options for cell-service in Korea: SIM Card I chose this option because it is cheap and there's a SIM Card provider in the dorm lobby so getting one is very easy! For a little less than $40 a month I get 15 GB of data. The only downsides are that your number will be changed to a Korean number and the plan is monthly, so have to go in person to renew your plan every month. Moreover, you will still have all your contacts associated with iMessage, but you will have to re-save all of your contacts that don't use iMessage. Wifi-Egg I have heard that the Wifi-Egg is useful, but it can also be pricey because the cost adds up over a four month period. You can use iMessage with a Wifi-Egg and you can access the internet, but you still will not have cell service so you won't be able to call or text anyone that doesn't use iMessage. Carrier-Provided International Plan You can ask your phone carrier to buy an international plan and all your services will be the same as it is back home, but it is a little expensive.
Adapter vs Converter
In Korea the electricity and outlets are different from the U.S., so you will need to buy an adapter and possibly a converter as well. An adapter just allows you to plug your cord into the outlet since it is shaped differently. It does not change the energy going into your device. If your device is not dual voltage, you will need a converter too. My iPhone and Mac have universal voltage; I think all Apple products are dual voltage. A converter changes the voltage going into your device, but it does not change the shape of your plug. You can buy an all-in-one adapter and converter if that makes it easier.
The convenience store in the dorm lobby sells adapters!