The Apple Store will allow the purchase of 2 phones per customer. So, if you want to buy a second one for your wife, you need to go to the Apple Store. (As earlier reported by iphonePOV, ATT stores will only allow the purchase of 1 phone per person) Here is more information from Apple's Announcement this morning:
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. Beginning Saturday morning, iPhone owners can learn how to get the most out of their new iPhone with free, in-depth workshops offered throughout the day at all Apple retail stores. Every Apple retail store will offer free support for iPhone at the Genius Bar and personal training through Apple’s new One to One program.Apple has also announced that as of June 30th, all Apple Stores will open at 9:00 (for at least the rest of the summer) to help meet the demand for iPhones.
“Apple retail stores were created for this moment—to let customers touch and experience a revolutionary new product,” said Ron Johnson, Apple’s senior vice president of Retail. “With our legendary Genius Bar support, free workshops and our One to One personal training, we’re here to help customers get the most from their new iPhone.”
UPDATE: Apple's online store will begin taking orders at 6:pm PDT on the 29th. Like most items this expensive on the Apple website, shipping will be free.