I am currently using a ZTE Zmax from Metro PCS using the factory settings that came with the phone. However, i have noticed that i can only send and receive MMS messages like pictures when i am using 4G LTE. When i am connected to Wifi the texting application simply tells me that the message could not be downloaded. This is a problem because it doesn't let me retrieve the message even after i turn on the 4G back on. When this happens i need to turn on 4G and tell the person to resend the message again. It gets annoying. I am currently using MYSMS as texting application. Not sure if this has something to do with it. I have had a similar experience with the stock messaging application. Could it be a problem with the APN settings?