Yesterday, Apple announced that the iPhone 4 comes to another 17 countries via its Retail and Online Stores, and also via its Authorized Resellers. These countries are: Australia, Austria, Belgium, Canada, Denmark, Finland, Honk Kong, Ireland, Italy, Luxembourg, Netherlands, Norway, New Zealand, Singapore, Spain, Sweden and Switzerland. This is going to happen this Friday, on July 30.
If you hope to get an iPhone 4 in one of the mentioned countries, you should pre-order (if it's available) it at an Apple Retail or Online Store, or at an Authorized Apple Reseller (the best is at the carrier which has an exclusive contract with Apple) as soon as possible, because there are expected important problems with stocks (and big delays, as Apple can't currently keep up with the request only from the US).
If you want the full article, view Apple's press release here.