An 'unknown issue' that has reportedly been plaguing what Apple calls "a small percentage" of the company's previous-generation smartphones as forced Apple into action resulting in free repairs for qualifying customers.
Apple said on its user-support page that "iPhone 5 models manufactured through March 2013 may be affected by this issue," in which the button, also known as a sleep/wake mechanism, stops functioning or works only intermittently.
Those affected by the bug that wish to have their phones serviced simply need to enter your device's serial number on the user support page that Apple has specially set up for dealing with this issue. Once you qualify — and we're not quite sure what criteria Apple is looking for in the "verify serial number" process, other than perhaps being phones from a certain release date or time frame - then you'll be able to drop your phone off at your nearest Apple Repair Center or mail it in to have it fixed.
Replacement of the sleep/wake button will have to be done at an Apple Repair Center. Giving users two options —carry-in or mail-in. Unfortunately the replacement process takes approximately 4-6 days from the time your iPhone is received at the repair center until it is returned to you. So expect to be without your beloved iPhone for up to six days as the Apple crew fixes it up. (If you require a loaner during the time that your iPhone is being serviced, participating Apple Retail Stores and Apple Authorized Service Providers MAY have iPhone 5 models (16GB only) available.)
Before sending your iPhone off for repairs you'll need to remove any cases, turn off 'Find my iPhone' and back up all your data as Apple is requesting that all customers erase all of the content and settings on their devices. Additionally, Apple has noted that if you are running iOS 6, your iPhone will need to be upgraded to iOS 7 after the sleep/wake button mechanism is replaced.