Working MMS on Straight talk
You have to have custom ROM for the straight talk MMS to work, but If do not want custom ROM, you have to be rooted, you can modify apn settings in System, and MMS will work. this is what you have to do.
Ist enter apn for straight talk, as given all over the web.
Second you have to have HTC M8 rooted, second get SQ Lite Editor from the app store (you have to buy it), after install open sqlite editor open Files tab/data/data/com.android.providers.telephony/databases/telephony.db and open carriers. Delete all carriers that are listed in them including at&t, but leave only Straight talk you have entered in apn setting earlier. Exit SQLite by going backward using back arrow. Reboot phone and you will having data and working mms on Straight Talk using at&t SIM.
I had used this method on HTC M8 (at&t variant) and LG Flex (at&t variant)
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