It was a valid question...one that she had an entirely other thread started about that was 2-3 pages long, but had spiraled down into answers she didn't want to hear because for some reason, she felt replacing the hardware over and over again would, some how, fix a network issue.
The last part of your post was a little strange to me though...the part where you said the iPhone was not good at transitioning from LTE to 3G during calls. Strange because VoLTE (which is available in the city that the OP said she resides in) is a brand new network feature, and one where transition is purely dependent on the carriers degradation of their own 3G service to introduce voice over LTE (which all of them did in order to start pushing this feature over more coverage area).
Where are you sourcing this info about the iPhone being unsuccessful at making the transition and simply dropping calls? As far as I've read (which is a pretty common thing honestly), there have been no wide reports of the iPhone, or ANY smart phones for that matter, having a particularly hard time making the transition, and that the issues observed in transitioning VoLTE to normal cellular calling have been purely focused on the carriers network boundaries for each service.