Doesn't that defeat the purpose when you want to just use Wifi? Whenever I lay my phone down for a few minutes and pick it back up, LTE is on the bar, then turns back to Wifi after a few seconds.
this has been an annoying "feature" for years
i turn my cellular off at home only because in the mornings i get a bunch of work emails that add up close to 50MB for the day
My 4 did this on iOS 4 too. It's by design. It puts the wifi functionality to sleep to conserve battery when the phones in sleep mode, unless you're actively sending/receiving.