Our recent vacation was, as usual, an investigation as to how our wireless phones work in foreign countries, and how to do it, cheaply. We threw a dart at the globe and picked Italy and it turned out to get there required travel through a number of other European countries. This requires a different mode of operation than using wireless in a single country.
I re-activated my T-Mobile Prepaid phone, primarily to make calls through their built-in Wi-Fi Calling app. This is a nice feature that you can make and receive calls through your US T-Mobile number at your normal US Prepaid per-minute rate. My regular phone, a Motorola, comes unlocked, but since it's not a T-Mobile branded phone, it doesn't have the Wi-Fi Calling app and you can't get it at Google Play. All our incoming calls were Call Forwarded to the T-Mobile phone.
Once we landed in Italy, I bought a SIM ($26USD) from a Wind store near the train station (We know Wind, they offers service in Canada). My phone needed to be re-configured manually (the APN) which they were happy to do at the store. Their SIM worked well and we used it for local calls and broadband. Right in town there was some 4G service, but more more reliably, 3G. Once we left town, service was only at EDGE levels, which was totally usable for email and location-based apps, like maps. It was faster than the Wi-Fi available on our Italo train.
After crossing into France, the Wind SIM worked for 24 hours with reminders to upgrade our service. After that, we still had coverage through the T-Mobile Calling app and Wi-Fi. The single-country SIM would have worked if we hadn't left Italy, but since we covered 4 countries, we should have purchased a Universal Roaming SIM. We saw these in airport magazine shops and Online. We used what we learned to completely re-design our International Roaming Pages.