Another option, and one that I've been using a lot, is to get a ThreeUK Sim Card. It works in 70 countries including all of Europe. And USA. It would be Data-Only in USA but can forward your GV to Hangouts for calls (both in Europe and Abroad), or shell out a little extra to forward your GV to the UK number that comes with it.

It's as easy as buying the SIM from Amazon, and sticking it into your unlocked phone. And it just works. Amazing.

I've been getting the $38 plan(https://amzn.to/357kMUq) which is 12GB over an entire year ($3/gig!), mostly using in HK and Colombia and quick Europe Trips. They've now got a $65/24GB (amazon: https://amzn.to/330ldy8) for two years as well. The one year plan was $50 just a few months ago, so somehow that price has dropped. Unbelievable. I keep expecting them to expand to more countries but seems they've peaked at the 70 or so listed. If you are going to any of those countries, it's def the easiest way to hit the ground running with data. The one month is like $20 for 10GB which is cheap enough that I've considered replacing my USA number with it and going Data only, but the Sprint Kickstart at $25 gets me a working number which makes life a little easier here.