Hello Kzabalawi,
Welcome to the community!
Firstly, the Fido Roam charge incurs when your device uses Fido Services abroad. That is, the charge will incur when you make/receive calls, send text messages or use data outside of Canada (see here). The mobile providers only know usage. If a device is using services when its settings are set not to use them, that's an issue with the device. The mobile providers have no access to a device's settings to know what settings are enabled/disabled. If you wish to receive text messages, there is unfortunately no 100% guarantee your device won't use other services and trigger roaming charges.
That said, there are things which can be done to prevent unintended usage. Ideally, enabling Airplane or Flight mode on a device or removing the SIM card would prevent the device from accessing the foreign networks. However, those actions won't allow the device to receive text messages.
If you do not intend on using data, disabling data and roaming data are also generally recommended to prevent unintentional roaming. Those settings would not prevent roaming for voice and text messaging. However, some device manufacturers might not prevent all data usage when connected to foreign networks (see here). That data usage would be considered roaming data. Customers would need to know how there devices behave when connected to foreign networks.
While receiving SMS would not incur the roaming charge, it's worth mentioning that the data contained within MMS (incoming or outgoing) would be considered roaming data and charged accordingly. You should note that MMS are not solely restricted to pictures or video messages. Messages with subject headers or group messages etc are also considered MMS. It should also be noted that iMessages and RCS messages are sent (and received) as data and not as text messages (SMS). In addition, it should be noted that the iPhone Voicemail notiications are sent as data.
Even if the text message received is SMS, if your device is configured to provide Delivery and/or Read receipts, those would be sent as SMS and considered roaming usage.
As already mentioned, making or receiving calls abroad will incur the Fido Roam charges. While letting calls go to voicemail does not incur any charges, you should note that checking your voicemail would incur charges as it involves calling the voicemail service.
For completeness sake, it should be noted that while using Wifi for regular internet access will not incur Fido Roam charges, there seems to be some misunderstanding regarding Wifi-calling. I'm not sure how people have gotten the impression that Wifi-calling does not use the networks. However, that is not true. While the calls and messages do not transmit via cellular towers, they still use the networks via the internet gateway (see image here). The cellular towers and Wifi are merely alternate means of accessing the networks. Calls and messages would not be able to complete or get sent/received without the networks. As such, using Wifi-calling is technically using Fido services. However, they have allowed certain usage to be free from additional charges. All the messages and calls you receive (from anywhere in the world) will be taken from your plan's voice minutes and messaging limits. As well, all Wifi-calling messages and calls you make to a Canadian phone number while abroad won't incur long-distance or roaming charges (see link above).
If you wish to receive SMS, there is unfortunately no absolute guarantee your device won't use other services and trigger roaming charges.
If you did not wish to use Fido Roam, you would need to opt-out of the service. In doing so, any usage abroad would be on a pay-per-use basis. You can view those rates here. You should note that this forum is community-driven and not intended as a venue for customer services. If you would like to opt-out of Fido Roam, you would need to contact customer service . In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Hope this helps 😀
Cheers
