It's a little unclear to me from reading the Wikipedia page; is it fully functional today, and worldwide? It'd be cool if my phone showed me which systems it was using at any time, but I have chosen The One True Apple Way so I don't think that'll come any time soon
If you're on Android there's an app, GPS Test that shows you a chart with all the signals it's picking up with different symbols for each system and a filter too. My phone is currently picking up 5 GPS, 4 GLONASS, 8 Galileo, and even 3 Beidou sat signals (I'm in Western Europe).
Also you should be able to look up your phone specifications to see what GNSS services it's capable of using on GSMArena
Edit:oh I missed that you're on Apple so that app is useless for you. Still might be of some use to others though.