"Apple announced a new replacement program today for folks having issues with the Sleep/Wake button on their iPhone 5. The program allows for the replacement of the button on select iPhone 5 models where it has either stopped working completely, or only works intermittently."
"Of course, your iPhone 5 must be in working condition to qualify for this program. The initiative covers iPhone 5 models [that meet the requirements] for 2 years after the retail sale date, and if you believe you paid for a replacement due to this issue, you can contact Apple for a refund."
Apple link ;
https://ssl.apple.com/support/iphone5-sleepwakebutton/Source : idownloadblog
http://www.idownloadblog.com/2014/04/25/apple-iphone-5-sleep-wake/