I think it could take as long as the christmas shopping season (day after thanksgiving to the 25th) for someone to wake up one morning and be able to get an iPhone with any hassle (ie calling/visiting multiple stores) or without getting lucky (ie checking at a store the day a shipment comes in).
I'm sure the the company building the actual product is working 24/7 to have as many iPhones as possible available at launch. After the intial launch i'm sure the production will slow down to avoid overtime costs and such.
All the being said, I could be overestimating the market for the iPhone. The high price point could drive consumers away, like what happened to the ps3. Limited availablity at launch + high price tag = lower then expected sales. And in the iPhone's case the you add in the other variable of other sub standard (yet functional and stable) cellphones being available for free. Razrs are now available for free with a 2 year contract. So the iPhone formula will read more like limited availablity at launch + high price tag + free alternatives + hype + possibly revolutionary product = ?
Should be interesting, I just hope i get one and that i'm not paying over 50 bucks a month for my plan.