Rooted ...S-OFF... running Viper One rom fixed it for me. I didn't wanna root my phone but I actually am glad I did. It's nice to get rid of all that AT&T bloat that I didn't use.
I updated yesterday. I have an AT&T HTC ONE that I'm using on Straight Talk. Now my mms isn't working at all. 3 hours with the amazing technical support of straight talk (i hope you catch that sarcasm) and still no help. I have the new 4g LTE sim card with the new APN settings that go with it...
I'm having the same issue. I dont use hangout either but I tried it just to see if it would work. It still doesn't. It is saying generic network failure. Looking for new apns that will fix it and I got nothing so far.