There have been a few reports circulating recently that the exclusive service providers in both Canada and Australia are running out of iPhones in stock. On top of that they are saying that it will be several weeks before normal availability will resume.
Although they are out of stock local Apple stores have most models available. Rogers Wireless, the exclusive carrier for Canada, stated that they are continuing to recieve new shipments but they are all going to fill backorders. This then causes all new orders on their website to be even further backed up. Apple also recently stated that they are having trouble filling all orders as a whole based on the extremely high demand.