For the first time since I got an iPhone almost two years ago, I'm travelling internationally (to Ireland and the UK). I've heard no end of horror stories of people racking up insane data roaming charges, which I obviously want to avoid -- but I'd also like to take normal advantage of having a smartphone (maps, dining apps, etc.). So what are my options? I guess the easiest would be to turn data roaming off and only use wifi -- though I don't know if free wifi is as easy to find as in the SF bay area. How complex is it to unlock an iPhone to allow use of a local provider's SIM card, to get cheaper rates? Any other options? In case it matters, I have a 3GS, and may or may not acquire a 4S before my trip. Thanks for any tips!