Just got back from Italy, Austria and Germany.

Italy was all over the place as to which carrier it would lock onto. Of course we stayed in an old monastery in Tuscany with foot-and-a-half thick stone walls, so data service was limited inside - unless I put the phone next to the window. I frequently would "drop" the data connection (just a voice connection), and had to force the iPhone off data and back on (turn data off, wait 30 seconds, then back on).

On the train going from Florence to Venice then on the night up to Munich (via Villach, Austria), had decent service (4-5 bars) using TIM - even in the tunnels - guessing that TIM is TrenItalia's preferred carrier...

Once in Germany, we took the train back down to Salzburg from Munich, and didn't have reliable coverage from any one provider (I have a blau.de SIM, T-Mo US SIM, and there were swaths where one had service and the other didn't). Trying to force to latch the T-Mo US phone onto O2 or E-Plus wasn't very successful. Being on a train, it wasn't a big issue. Salzburg had decent service on T-MO Austria (slow, but seemed faster than in Italy or Germany).

Can't complain - the Edge-level speeds work fine what I was doing on the phone (voice, text, Facebook and Maps). (I did have a TIM Welcome Internet SIM in Italy, and have a Blau.de SIM for Germany for my iPad for the serious surfing - like downloading some music/podcasts...).

J