We're not all equal around the globe when it comes to buying an iPhone 4. Besides the various delays (for example, from 3 days in France, up to 8 weeks in Switzerland), the prices vary quite a lot. Of course, it mostly depends on the carriers, but Apple's unlocked devices don't cost the same everywhere.
To give you a little overview of the disparities, one reader over at iFun.de put together a comparative chart. As you can see above (or by hitting here for the iDevice-friendly pdf), it can often be well worth it to order your iPhone 4 in a different country (you'll need an intermediary), or even just going across the border. Also, it will give you a little idea of what kind of margins some folks are making on Ebay.