I'm trying to get Vodafone to send me the APN settings OTA but it seems their website stopped being updated with the Samsung SIII:
freitasm: Don't worry - working now! Sent a message from the S5 but instead of using "Gallery" to select a photo I used "Photos" and it converted and sent it...
Channel Manager, Help & Support @ Vodafone NZ
I just got my S5 and haven't actually tried MMS yet, but I always had a similar issue with my old S2 (last Touchwiz device), when sending from the Gallery people who were on VF wouldn't receive my MMS messages, but people on Telecom would which made me think that the two networks could have different max MMS sizes. The Samsung Messages app doesn't have any options for setting the max image/attachment size like the stock Android one does.