Hello Hoss123,
Welcome to the community!
As you appear to be aware, 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. It should be noted 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). 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 or data and considered roaming usage.
Unfortunately, I don't believe it is possible to disable MMS at the network level. However, you should be able to disable MMS on your device. The method to disable MMS would depend on your particular device (see Android and iOS).
It is generally recommended to disable data and roaming data in order to prevent roaming charges. However, it should be noted that the disabling roaming data does not prevent roaming for calls and messages. In addition, it should also noted 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. For example, while disabling data and roaming data should prevent data usage on foreign networks, some mobile manufacturers (ie Apple) does seem to allow some data usage despite those settings disabled. And no, it doesn't seem to be a Fido issue. It happens with multiple providers as well (see here).
That's why in order to prevent roaming charges, it is also usually recommended to keep Airplane or Flight modes enabled for the duration of trips. Customers could manually enable Wifi when required. I understand doing so would also prevent incoming SMS or emergency calls.
Fido Roam is enabled by default on most current post-paid plans. If you did not wish to avail of the feature, you would have to opt-out of Fido Roam. In doing so, any usage would be on a pay-per-use basis. Those rates can be found here. Alternatively, if you did not wish to use any services, you would could request to have roaming blocked on your account. You would need to verify which option is applied to your account as some customers had assumed they requested a total roaming block only to find pay-per-use usage abroad (opt-out Fido Roam).
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).
You should note the forums are community-driven and not intended as a venue for customer services. If you wished to discuss your matter and/or opt-out of Fido Roam (or apply roaming block), you would need to contact customer service.
Hope this helps 😀
Cheers
