For anyone who wanted to use the phone outside the six networks officially sanctioned by Apple it made things easier. By simply buying the phone with no service they avoided the hassle (and early termination fees) typically associated with cancelling a contract.
In order to bring prices of the iPhone 3G down they've adopted a different plan. Rather than selling the phone directly they're counting on service providers to subsidize the price, which means buying from a company like AT&T rather than directly from Apple. As is standard with such deals, customers will be required to sign up for service with the purchase of the phone.
Of course you can simply sign the contract and then cancel it after the purchase. While this typically results in an early termination penalty, in most cases the final cost (including the initial purchase and penalty) will probably be close to what you would have paid if you could buy it directly from Apple. For example, given AT&T's $36 activation fee and $175 early termination penalty the total cost of a $199 iPhone after cancelling the contract comes to $410. That's just a little more than the $399 pricetag for a comparable (and unsubsidized) first generation iPhone.
With the iPhone 3G being launched in 22 countries initially and 48 more by the end of 2008, the good news is there should be less demand for unlocking. But if you happen to live in one of the countries where exclusive carrier deals will still be in force, including the United States, United Kingdom, France, Germany, Spain, and Ireland, getting an iPhone to use on another network will require some extra effort - not to mention a little extra cash.