Hello G35C,
Welcome to the community!
As far as I am aware, both of those options should allow you to roam internationally (note the Basic monthly plans do not allow roaming). As already mentioned incoming SMS do not incur any roaming fees. However, you should note that any data contained within a MMS (incoming or outgoing) would be considered roaming data and charged accordingly.
You also should note that multimedia message services (MMS) are not limited to just photo or video messages. Some phones allow users to add Subject lines to their messages -- similar to the subject lines found in emails. Adding a Subject line automatically converts a SMS to MMS. A blank subject line may also still be considered a MMS. It's possible your phone is automatically including a subject line (blank) and sending those messages as MMS. You might consider disabling any automatic MMS download settings in your phone. You would receive a SMS notification (no charge) with the option to download the message. You should further note that with the exception of Wifi-calling, MMS do not generally transmit via Wifi. Connecting Wifi (and the networks) in order to download the contents would result in the MMS downloading via the networks and roaming data would likely charged.
If you currently have a post-paid plan, you would be able to migrate your services to a pre-paid plan. However, you should note that there would be a migration fee for the transfer.
If you decided to stay with a post-paid option and did not intend on using Fido Roam, you might consider contacting customer service to opt-out of the 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. In doing so, any usage abroad would be on a pay-per-use basis. You can view the roaming rates here.
Hope this helps 😀
Cheers
