(Wow, lots of us posting at the same time, popular thread)
Of my various European adventures, though, I've found that I don't actually use my phone much because it's so shockingly expensive ($1.29/minute, I believe), versus just using Skype or whatnot. Maybe I could ditch the phone altogether, but certainly I can't discount the need for a phone as an emergency device.
When I went to the empeg meet in 2004 with my T610, I bought a prepaid SIM in London to use. Calls were way cheeper for me that way, as most of my need for a phone was to call other people in Europe. Having my own phone was nice, as I still had my contact list. Now with smartphones, that probably even more important, though AT&T won't unlock the iPhone like they will other phones.
If I were to travel over there again soon, I'd probably go a similar route of picking up a prepaid SIM with data. I'd use Skype for calls back home, and normal voice for calling local places. I'd definitely need the phone for emergencies if I did similar activities like I did in 2004 (riding around on a motorcycle in the Alps).
Random side note, thanks again to everyone who let me stay with them, or showed me the areas where they lived. That trip in 04 is still one of my fondest memories.
If using data while you're on a call really is that important to you, then you can only go with a GSM carrier (is it possible to even do this on the EVO? I hadn't heard if their 4G implementation was capable of it).
I had assumed wrongly it seems. I was under the impression the phone uses 4G only for data and 3G CDMA for voice, and that still seems to be true. But it still doesn't allow both to be used, according to the FAQ on Android Central.
Here's the official line direct from HTC: "If you're using 4g for data, you can't use CDMA for voice. currently the only way to do simultaneous voice and data would be through a third-party VOIP solution. However, this is not do to strict hardware limitations, so it's possible this could change with future updates."