While all three are MVNOs operating under Singtel, their roaming partners may differ. Generally, data roaming allows for automatic scanning and connection to the strongest available network. However, if you need to manually choose a more robust network, you can select from a list of partner networks in the country you are visiting.
ZYM Mobile
Indonesia : Telkomsel, XL
Malaysia : Celcom, Digi
Thailand : AIS (AWN), True Move, DTAC
CMLINK
Indonesia： XL, Hutchison 3, Indosat Ooredoo, Telkomsel, Smartfren
Malaysia：Celcom, Digi, Maxis, U mobile
Thailand ：AIS (AWN), True Move, DTAC
ViViFi
Indonesia : XL, Hutchison 3, Indosat Ooredoo, Telkomsel, Smartfren
Malaysia : Celcom, Digi, U Mobile
Thailand : AIS (AWN), True Move, DTAC