Hello Spirit84,
Welcome to the community!
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). I understand you will be turning your data roaming off. You should note that disabling data and/or roaming data does not prevent roaming charges for calls and/or SMS.
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.
You might consider disabling any MMS auto-retrieve settings on your phone. You would then receive a SMS notifying of a MMS (no charge) but the data contained would not download automatically. You could then choose whether or not to download the associated data contents.
As already mentioned, making or receiving calls 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. I posted a brief summary here in response to similar questions.
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).
Generally using Wifi for regular internet access will not incur Fido Roam charges. In order to prevent unintended roaming charges, it is usually recommended to enable Airplane or Flight mode for the duration of your trip. You could then manually enable Wifi when required. That said, I do understand those modes would not likely allow you to use your device with a local eSIM.
If you did wish to use your device with a local eSIM, you would need to know how your device behaves when roaming. If your device is dual-SIM, that functionality is not standardised. It may not operate the way you think it does. You should also note that some phones might consider certain system data differently from user data and continue to allow the former usage despite data and roaming data settings disabled. The mobile providers can only know a device's usage. They have no knowledge or access to a device's settings. If a device uses services without the customer's intent, it is still considered usage and would incur roaming charges.
Hope this helps 😀
Cheers
