An iPhone 4 not subsidized by a carrier contract will be costly, but it still actually is cheaper for those who spend a lot of time out of the country. They will be getting the iPhone 4 sans contract, and will use local service in the countries they visit, either through a regular wireless account or through prepaid SIM cards. Well, if they can find local micro-SIM cards that is.
I personally will probably still sign a contract to get a subsidized iPhone 4. However, given Fido's annoying stacked contacts, I'm also considering going to a new carrier for my iPhone 4 after my current 3G's 3-year contract runs out, but only if they can offer decent voice and data plans. Fortunately, the big three in Canada - Rogers, Telus, and Bell - all offer the iPhone now.