It looks like Sprint has removed the iPhone 4, 4S and 5 from the blacklist of phones that Sprint MVNOs aren't allowed to activate, see article below.
http://www.prepaidphonenews.com/2014...s-are-now.html
Also the HTC One and Samsung S4 can be activated to Expo, there isn't much information on
www.ExpoMobile.com but can any other carrier activate the iPhone 5C ?