Hi guys!

MIA has different frequencies for approach, departure, arrival, ground, flight advisories and etc. Not to mention different ATC handlers for every sector. I'm not really an expert on this one because this is an ATC thing and my radio license doesn't cover this so I won't go deeper. and yes, all civilian aircrafts and airports in the world still use VHF-AM. AFAIK, other militaries like the US use UHF.

I do notice that, the disadvantages of AM radio is diminished when you increase in altitude.