In a new press release posted today on Apple.com the company clarifies how iPhone sales will work tomorrow. In the release, Apple states that iPhone goes on sale at "6:00 p.m. local time at Apple retail stores nationwide. All 164 Apple retail stores in the US will stay open until midnight, and customers can purchase up to two iPhones on a first come, first served basis."
The actual number of phones allowed per person is the new information in today's release. Previously it was rumored that Apple and AT&T were implementing a strict one iPhone per person rule for tomorrow's sales. This was a disappointment for those looking to purchase an iPhone for a spouse or a co-worker.
Since iPhone doesn't require in-store activation, some sort of cap was necessary to eliminate the inevitable hoarding that would come if no limits were in place. The two unit cap is more than reasonable and should stem the amount of iPhones that will end up on eBay, although it's bound to happen.
The other new information in the release is that Apple will be providing training and support on iPhone beginning on Saturday and that Apple retail stores are opening early (9 a.m.) on Saturday for iPhone sales. This is a departure from most malls which open as late as 11 a.m.
Update: It appears that only Apple is allowing two iPhone purchases per customer. Three AT&T retail stores that I called said that they have a strict one-iPhone-per-cutomer policy.