Apple recently enabled its reservation system for online customers looking to buy an iPhone 5s. Shortly after going live, the company removed this in-store pickup option. Apple's website now says that the iPhone 5s is not eligible for pickup and that all purchases must be made in the store.
We don't know why Apple did this flip-flop, but it's possible that the reservation system went online earlier than planned. Apple typically has sold new iPhones in the store on a first-come, first-serve basis for the first few weeks after launch. Once demand and supply start to even out, the company then enables in-store pickup on its website. It's also possible Apple will turn on the option and turn it off as inventory ebbs and flows.
If you are still on the hunt for an iPhone 5s, your best bet is to keep checking back with Apple, your wireless carrier and retailers like Best Buy, RadioShack and Walmart. It'll take time, but your persistence will pay off eventually.
Hat tip to David for the tip.