I think there are no easy fix for your problem as I also encounter with da mms problem, I learn to download mms manually.... and then keep changing my mobile network setting when i want to download or send mms.

what i will always do is first set my mms setting to manual, go to setting > wireless & network > mobile network set my network mode to GSM / WCDMA

after that quickly go to *#*#4636#*#* > phone info > set prefered network type to GSM/CDMA auto

then go to preferd mms msg n download

hope it will help ur problem a little