I still don't this is easy. First, the new T3 has changed locations. I arrived from LHR. In the old terminal there was one right before the elevator down to passport control. Now it's landslide. When you exit, turn right, as if going to take the train to the city. It's on the right, just before you get to the escalator to go down to the train.
Just topping up the data would be cheap, but I need to meme phone calls in Italy and to the USA, when not on WiFi. That is not cheap. Also, something weird happened. My SIM card was showing a different phone number than my usual Italian number. I've only had one SIM. We couldn't get it to work, so I had to buy another SIM card. As usual, 30 minutes at the counter. It's never easy for me. I will say the line wasn't bad.
The new T3 is great. I didn't have much time to explore but it's huge, uncrowded, bright and glittering. Very nice terminal.