I am using an iPhone 4 with iOS 6 and have not experienced this disconnect of WIFI during sleep. After reading all the threads here, I decided to see if what others claim to be a fact that it does because it's supposed to I did some testing of my own. I find this would be really stupid for Apple to setup iOS to lose WIFI during sleep strange for several features wouldn't work. On my iPhone 4 I streamed some music using an app called TuneIn Radio Pro (which gives you a WIFI/cellular counting within the app) and began with WIFI connected. I manually put it to sleep and streamed for 5 mins or so. I unlocked the phone and checked the readings, and there's was only WIFI data downloaded, and my cellular was still at 0. To double check this, I went into the iPhones settings and checked there as well, and again no cellular usage was increased before the streaming over WIFI. I DID NOT have the iPhone plugged into power either it was solely on battery. Another situation I have proved this to not happen.....I have the new iPad WIFI only and stream videos via Airplay to my Apple TV with the iPad in sleep mode once I start the video stream, and again, no issues of disconnect. For Apple to design iOS to lose WIFI during sleep would be plain stupid for iDevices that do not have a cellular ability such has streaming music thru a docking speaker system, it doesn't make sense to leave your screen on all the time to stay connected to WIFI as this would drain your battery faster the the WIFI connection. I am not saying that as long as no apps are accessing the WIFI connection there may be a disconnect then, but as long as there is data being transferred during a WIFI connection and the iDevices sleeps, it should continue to use that source.