It is possible to do txt and MMS messages over wifi. I know this works on iPhone's on at&t and Galaxy S3 on Sprint. I took for granted that all carriers supported this on all devices but apparently not. Neither of my fiends who have a GS3 on Vz or at&t can do txt/MMS over wifi. My one friend on at&t was doing this on his iPhone just prior to converting to a GS3. It's easy to test this by putting your phone in airplane mode and then turning on wifi.