What caused the dropped calls?
As i've said previously - I'm in a rural area of Ireland and there are a number of cellular black-spots in the area and cellular reception fluctuates even though we recently got 4G / LTE in the area - you can frequently find your device fluctuating between LTE/3G/2G.
Whilst other devices I've had have also suffered from dropped calls at certain times - it inevitably happens here - especially on my daily routine of travelling to the nearby beach 3 times a day. Other devices might drop a call once every day or two, even when passing through the black-spots whilst reception will phase out and I won't hear the other person, usually it will manage to stay connected and after I've gone through the area a few seconds later we will be able to continue talking.
The M9 unfortunately just couldn't seemingly jump between networks as easily or reliably and when doing so would drop the call on me. Even in areas where it shouldn't be an issue - it often was and it was irksome having to constantly apologise to people - even when it started to become a running joke with the other caller.
I'm sure if you lived in a town / city - an area where there was a stable cellular reception generally it wouldn't be an issue - but for me it became too much of an inconvenience (especially when I had to ring back people on different network and use up my minutes / incur charges).