Earlier quoted context omitted.
I'm on an MVNO who doesn't care, but the settings for the network the MVNO runs ontop of override it with a different APN. It's times like this I really hate Apple's operator-relationship BS.
I hate how they make it super hard if not impossible to override the APNs yourself... I change carriers every month, and do all sorts of odd stuff with my SIMs, and my iPhone chokes on them because of it :(
I'd be surprised if there were more than a handful of people actually doing this, which would explain why your use case doesn't get substantial engineering/UX resources.