I have an HTC Android phone with Verizon and called them before my Europe trip to see if I could use it over there. The guy enthusiastically said no problem and shipped me a new SIM card. We spoke after I installed it and things weren't going well but he assured me they would have it working before my trip. Just days before I left I got a text from Verizon telling me the plans were all active and in place.
Since I'm a belts and suspenders kind of guy I didn't trust them so got in on that 2 phones from Eurobuzz deal (turns out they are really Mobal out of the UK). When I got to Europe I turned on all my phones. My wife's Verizon iPhone worked fine, my two Eurobuzz phones worked fine, my phone was a brick. Good thing I had my plan B ready. In fact, I had a plan C too - brought along a cheap unlocked quadband phone so I could buy local SIM if needed.