My phone won't receive picture messages when on wifi?

Hey! So my phone won't receive picture messages from literally anyone with any phone unless cellular data is turned on. But I use wifi when at home and i don't like to use cellular data unless I'm away from home. This also goes for videos that are longer than a minute. Does MMS just not work when on wifi or something? Because if so, I'll never know if someone sent me a picture or video longer than a minute since I only use cellular data when away from home.