VOIP over 3G Coming to the iPhone
Apple updated the iPhone software development kit on Wednesday to allow internet telephony apps to work on the 3G network. The little-noticed move effectively unlocks the ability for the iPhone — and the upcoming iPad — to be used as web phones.
That will help tremendously here in the US - of course, while traveling, you would still need a (pretty darn expensive) data plan to use Skype over 3G. It's progress though.