How can MMS be downloaded via wifi connections? I do not have data but have MMS as part of my phone plan, and am unable to send/receive any picture messages (It says downloading until it errors with no useful information).
You can't download MMS in any way other than a cellular data connection. What you could always do is while connected via wifi (so that your apps don't use the cellular connection) re-enable your cellular data to get your MMS messages.
Keep in mind if any apps use the cellular connection you are responsible for their data usage.