Apple recently updated its iPhone 5 Sleep/Wake Button Replacement Program page, as noted by Apfelpage [Google Translate], adding an additional year onto the service. This will allow customers with a malfunctioning iPhone 5 up to three years after purchase date to replace the sleep/wake button on the device.
The service began last April when multiple reports surfaced concerning the iPhone 5's lock button only sporadically working, or ceasing to function altogether. The program allowed customers to enter their iPhone's serial number to confirm its eligibility and subsequently carry-in or mail-in their device to be fixed in 4-6 days.
The new extension brings an additional year of coverage onto the service for iPhone 5 users facing faulty sleep/wake buttons. As a few redditors have noted, the service may require replacing more than just the lock button.
I had mine fixed through this program. They changed all the buttons and replaced my battery for free too. Once you get your phone back you can ask the guy at the apple store for the list of parts that were replaced. I think they have to replace a few things in order to get to the button.
The company did the same for its iPhone 5 Battery Replacement Program last week, as spotted initially by iPhone in Canada. The program was set to expire on March 1, 2015, "or two years after the first retail sale of the unit." Apple added a third year onto the program, extending the iPhone 5's battery replacement program into 2016 as well.