Apple has lengthened the shipping estimates for the iPhone 4 to between 1-3 days on their online retail store, likely ahead of the widely speculated iPhone 5 launch in October. It is possible that inventory numbers could be running low on the iPhone 4 because of the larger focus being on the production of the iPhone 5. The current iPhone was previously shipping within 24 hours, but the longer shipping estimates are now found on both the U.S. and Canadian online Apple retail stores. The same shipping delays have also been tacked on to the iPhone 3GS, which Apple has been selling for over two years. The iPhone 4 still appears to be shipping within 24 hours in other countries such as the United Kingdom and France.
UPDATE: It turns out that there were widespread shipping delays on almost every Apple product offered on their online store, but all estimates, including the iPhone 4, have returned to their normal time frame.
UPDATE 2: Apple now has products listed as “in stock” in lieu of precise shipping estimates.