Adding to a few good ideas, you'll not be needing that iPhone 4 in Europe - there's no SIM for voice or data, if you really want to bring your VZW number with you, consider buying a VZW world phone online, you'll be spending between $125-$150. If you must have data, look for a used HTC Imagio - it's old WinMo 6.5.1 with Sense, but it's got the right radios for Europe and VZW will still activate them for use in Europe (if the ESN isn't bad). If voice calls are the only thing that matter and you want to bring your VZW number with you, one can still find a new Motorola Z6C or Samsung Renown or LG Fathom (all of which VZW will activate for use in Europe), and I've seen the LG new for about $100 on Amazon.
Or spend way more and upgrade to a shiny new iPhone 4S...