I just got back from a trip to France with my AT&T Pre+, using a local SIM card. I can't tell you how frustrating it was going back to 2G speeds, since the Pre+ will only do 3G on the U.S. frequencies.
Now, if I'm reading the specs correctly, the GSM Pre 3 that passed the FCC is also only using U.S. frequencies. I'm on AT&T specifically because I travel a lot and wanted to have a GSM phone for that reason. Ironically, it looks like the only U.S. Pre 3 that will get 3G in Europe is the Verizon version. How bizarre is that? This seems like a pretty stupid mistake. My old GSM Treo Pro was 3G in Europe. What is HP (or is it AT&T?) thinking?