The iPhone worked well on the trip to Austria, including the layover in Copenhagen. Reception was always strong, even as the carrier would switch as we crossed the country. Convenient to send text messages (SMS) to my family in the States to keep them up-to-date on our location, to check email, and to send pictures. I didn't do any web surfing, but assumed it would have worked well.
Paid for the international plan before leaving, waiting to see how that worked out :)
EDIT: oh yeah, it was also an excellent alarm clock and world clock - I setup 4 clocks, one for each timezone we had family in (California, England, Japan) and one for where we were at the moment. But the phone always knew what timezone we were in anyway, even when DST kicked in the morning after the wedding. It was very annoying to go through 2 DST changes.
The address book was always easy to use when adding contacts made at the wedding.