Apple is offering repairs for fault sleep/wake buttons. You will have to navigate to Apple’s recall program website and enter your iPhone’s serial number. (Settings > General > About > Serial Number) to check if your device qualifies. Please know that this only applies to iPhone 5 units with a faulty sleep/wake button.
Go here to check if your iPhone is eligible for repair: (URL) https://ssl.apple.com/support/iphone5-sleepwakebutton/ (Link)
If your iPhone qualifies, you can have Apple repair it free of charge.