Apple, copying others and calling it magic since 1976!
Which seems weird that you have no way of preventing it from happening.
The interesting thing is that apparently you don't even have to open the message for the attack to work--they can just send it to you and it takes over your phone.
I've also been tempted by the Fire phone, but can't get past all the negative reviews. Apparently, if you turn off all the special display features, it operates okay. There's also a way to backdoor...
I don't think it's a phone or operating system problem. It's a network, poor reception problem.
Have you tried unlocking the phone through their website as a non-ATT customer? That usually works unless the phone is still under contract or not paid in full.