Earlier quoted context omitted.
I'm sure that's AT&T. I'm in Australia and there's been no such problem personally or from anything I've heard.
I've had issues on Telstra. Sometimes the phone UI will prevent you from answering the call. Sometimes the phone crashes mid-call. Sometimes you answer the phone and you can hear the other party but they can't here you.
I don't know if it's the phone or the network - I haven't done much testing. It's quite irritating pressing the answer button repeatedly and the phone not answering the call, or when I call someone and I end up unable to hear them while they can hear me.