Updates for future readers:
We were in the UK and Ireland for two weeks. The phone IS unlocked, but VZW keeps giving all sorts of weird messages, clearly it's not happy when you pull their card out! lol We used three.co.uk based on advice from those who live there: very good and fast service pretty well anywhere. We did get spotty up in the nether north parts of Scotland and the southern coast of Ireland at times, but otherwise it worked great. You can buy a 30 pound card that you'll likely not use up with 12 gigs of data and so many minutes of phone and texts we didn't even touch the limits. Used like a half gig! even with all the navigating. Once you sit somewhere, wifi is pretty prevalent, so you really only use of data when navigating. If we were to ever go back, we've got 95% left on our cards...it did take some set up by the 3 guy to see their network, but after that no trouble. And returning to US, just plugged back in the VZW cards and all was as it had been.