For most of this first week of iPhone 5 sales, purchasers had to walk into the Apple Store and buy on a first-come, first-served basis--or wait for online orders to be delivered by mail. But as , customers will be able to make their purchase online starting at 10 p.m. Tuesday; stores that have reserve inventory will hold the purchase for next-day pickup.

Interestingly, Apple's website will only make those next-day reservations available for night-owl customers--people who do their purchasing between 10 p.m. and 4 a.m. The company hasn't explained its logic, but its assertion that "limited quantities" may be available for walk-in customers suggests that the big opening weekend of sales may have left stores with limited inventory: Some outlets may not know until the store is closed for the day how many phones will be available for next-day sale.

Purchasers who want to reserve an iPhone 5 for in-store pickup will need to do so directly with Apple. A Verizon Wireless spokesperson said that her company's in-store sales are made on a first-come, first-served basis--online orders are delivered through the mail only. Representatives from AT&T and Sprint did not respond to inquiries; , however, makes no mention of reserving a phone for in-store pickup. Similarly, lists the different varieties of iPhone 5, but tells customers they can be purchased "in store only."

iPhone 5 buyers who do arrange to pick up their new phone at an Apple Store should be prepared: They must bring their old phone--if replacing it--along with their Social Security number, government-issued photo I.D., and carrier account password, if they have one.

Purchasers aren't limited to buying through Apple's website: Purchases can be arranged on an iPhone or iPad using the . Phones purchased online must be picked up in the store within 24 hours.