Texts, both SMS and MMS, must be sent over your Carrier's network. The SMS's are sent over 1G just like a phone call and MMS's require a data connection. The data connection for the MMS messages must be carrier not wifi. MMS messages are not counted against your data usage, but they do count against your message limit, if you have one. Your phone is supposed to be able to "referee" the connections when you are on WiFi to make this work seamlessly. I do know that if you turn off your 3/4G capability in settings while on WiFi this will cause issues with MMS messages but not with SMS messages. Also, there is a AV package from Kaspersky, that changes the settings on your WiFi connection and the changes that it makes cause MMS's to not send. I know there are no answers in this, but maybe some of the info will give you a direction to look. I have only had issues associated with the Kaspersky thing, they are aware of it and are working on a fix, but I just set my WiFi settings back to normal and rectified the situation.