What business do mobile phones need to open in Thailand?

To go to Thailand, mobile phones must have international roaming service. Suggestion:

1. To open the international roaming service of SIM card, you need to contact the operator.

2. Need to verify whether the local network frequency band matches the mobile phone.

3. After confirming that the above two points are met, open the phone settings/settings-More networks-Mobile networks-Data roaming. (Settings-Data Usage-Menu Key-Check Data Roaming)