Welcome to the community!
Firstly, what plan-type do you have? In addition, what phone do you have? You should note some plans (ie Basic Plans) do not allow for roaming.
The Fido Roam charges will only incur if your phone uses services -- make or receive a call, send a text message or use data abroad. It should be mentioned that while receiving SMS would not incur the roaming charge, any 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 further be noted that iMessages and RCS messages are sent (and received) as data and not as text messages (SMS).
As far as I am aware, having calls go to voicemail and/or rejecting calls to send them to voicemail should not incur roaming charges (see here). However, checking your voicemail would be considered roaming as one must call the voicemail service.
So receiving a SMS and receiving voicemail should not incur roaming charges. However, sending text messages and checking your voicemail would likely incur those charges.
If you have a plan and device supported for Wifi-calling, that service may be an option. 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 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 😀