Apparently M1 has pay-per-use roaming service, which does not have subscription charges and activation fees, and is enabled by default. With this I should be able to connect to overseas telcos and receive SMS (free) and not incur additional costs if I don't send sms/make calls.
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Pay Per Use Roaming (PPUR) allows you to use your M1 Postpaid for calls and SMS when you are overseas.
If you subscribe to PPUR, any roaming calls and SMS usages are chargeable at 20% on top of prevailing roaming rates. There is no registration fee nor monthly subscription for PPUR.
This roaming service is ideal for occasional travellers.
Pay Per Use Roaming (PPUR) is enabled by default on all Bespoke Plans. No activation of Pay Per Use (PPUR) is required."