you always needs to manually edit APN's to get working MMS on MVNO's. how you do this depends on your phone, but will never be an automatic thing.
you will never have much luck getting this fixed through a CS agent. best option is do your own research(forums are your friend) or find a small shop thats unlocks and flashes phones to get help with proper APN settings.
You, were answering to the wrong person. I have edited my mvno's on all the phones on one phone it was working in the evening the next day it didn't and the phone was never changed or turned off. GoSmart is having difficulties getting MMS working properly and they have admitted so.