If you need continuous access to the Internet and mobile communication, it is recommended to get a local SIM card.
They are sold in all supermarkets and shops with mobile phones; it is possible to recharge a balance there. You need to have only the passport. The tourist SIM card is adjusted in several minutes and is valid for a month. The recommended operators are Telkomsel and XL Axiata. The code of the country is +62, for internal is used 0.
You can check your balance by dialing * 888# for Telkomsel and * 123# for XL Axiata. The international Telkomsel line is 01017 (001 or 007), then a country code, XL Axiata – 01000, then a country code.