@89461
MMS attachments require active cellular data to work. They won't work (and can sometimes be "lost" indefinitely/forever) across most WiFi connections. I don't understand exactly why, too many variables (along with too many unknowns) in the tech.
But MMS attachments are not counted towards (billable) data allocations. They'll be logged on your Self-Serve usage history as "MMS data events" which consume 0MB each.
iMessage, RCS, and other msging apps which layer extras onto basic SMS/MMS functionality might work on both Data and WiFi. But beware that these text-over-data apps are not recognized by the network as "MMS data events" so they will consume billable data when they use it. Best to test for yourself before relying on it, send and receive a few attachments then login Self-Serve a while later and see what it says. I know you don't get a lot of Data on $15 Plan (even with the free holiday gift Data Add-on which you should collect, if you haven't already).
Your phone needs to be configured with Public Mobile's APN settings (with "APN Type" = "default,mms", lowercase no quotes no spaces)... then restarted... then have data turned ON. If data is turned OFF then you'll only see upload/download placeholders. Public Mobile (Telus) seems to store up to 10 "undelivered" attachments on the network for at least a week before they're overwritten or discarded - but I haven't really tested the limits exhaustively.
https://productioncommunity.publicmobile.ca/t5/Phones-Hardware/How-do-I-set-up-data-APN-on-my-smartp...
