As an American who likes to travel to Europe, this is a godsend. I can buy a pre-paid SIM before I leave America and then use it all over Europe. Getting a TIM (Italy, 35 Euro for one month) SIM was a real pain in the ass and I would love to have found somewhere else to make the process much easier and cheaper.
You could also just use Google's Project Fi. My biggest complaint about them is it takes about 10 minutes to get an LTE connection when switching continents (which is basically to say I have no complaints).
