Automatic Roaming Information

Automatic Roaming Service - This service allows you to use voice and video calls, SMS, and data services overseas without changing the setting of your mobile phone. 
(Video and data services are not available in some countries.)
WCDMA Roaming : WCDMA network, which is the global standard that is most widely used, allows you to use voice calls / video calls / MMS / Data services in WCDMA regions such as Japan, Europe, etc. with the same number you are using within the country. 
However, there may be limited coverage in WCDMA regions other than Japan. GSM Roaming : Unlike the domestic 2G, GSM service is being used in the U.S., Europe, and parts of Southeast Asian countries, and voice and SMS services can be used during automatic GSM roaming. However, mobile phones equipped with GPRS can use MMS services in regions that have GPRS data service.
If you would like to use automatic GSM roaming, you must use mobile phones quipped with GSM features such as SPH-W2500.
* GPRS is a 2.5 generation mobile phone that enables high-speed internet, video calls, etc.