No matter what you use, I had an experience on my current Vienna trip that reminded me to go through GV or WhatsApp when making a telephone call. I have a SIM through Tesco Mobile Ireland which I've used for several years now on various trips to the EU, especially since June 2017. If I top up by 15 euro or more, I get a data bonus. When I arrived in Vienna, I called back to the US to touch base with my office. I made the call through the phone's regular app without thinking (shouldn't be making decisions after a poor night's sleep on a plane!). Seven-minute call, 15 euro wiped out of my remaining call credit. Quickly topped up online and remembered to make the next call through GV--fifteen-minute call used up less than 25 cents of Google call credit.

I hate to learn through stupidity, but I really like the combination of an EU SIM and GV.