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Or configure your MMS. Most often the phone does this automagically, but, especially with mvnos, it can fail to get set up properly.
Do a web search for "<carrier name>" mms settings" and save the page or copy down the values.
On the phone - go to Settings > cellular + SIM > SIM settings > edit MMS APN and make sure the values match the ones from your search.
IF you have a Verizon phone that is running on another carrier... Verizon may have removed your abilities to alter MMS.
For more help, start an account here and reply in this thread.
Will that eliminate having to toggle the cellular all the damn time? I've always wonders how that worked and I still don't.
Verizon. When on wifi, I still can't retrieve pics or vids via text. I have to switch to cellular download it then switch back to wifi. I have an Icon with PFD 8.1 by the way.Ya know... I never thought about it, but YES your phone should just use cellular for MMS even though WiFi is on. To test I connected to WiFi and I was able to send and receive MMS. Lumia 1520.3, Official 8.1 + Lumia Cyan, Straight Talk AT&T compatible SIM.
Who is your carrier?