Apple offered to replace some older iPhone 5 smartphoneswith flawed on-off buttons.The California-based company said a "small percentage" of iPhone 5 modelsmanufactured through March of 2013 may have on-off buttons that stop working orwork intermittently, in a posting on its support website."Apple will replace the sleep/wake button mechanism, free of charge, on iPhone 5models that exhibit this issue and have a qualifying serial number," it said at thewebsite.The support web page contained instructions for iPhone 5 owners, along with a wayto check serial numbers to determine if smartphones qualify for free repair.The replacement process began Friday in the US and Canada and will begin in othercountries on May 2, according to Apple.