Hi Personally I have seen the Wi Fi connectibity specially on the 4S
and even you could see on the apple vis forun
One friend of mine needed to go at apple store to replacement twice the 4S and not only the Wi Fi as Bluetooth well.
I have using an iPhone 5S and I haven't seen any bugs with the 5S even I had an iPhone 5 and many issues occored on the connectibity on the 5 but everybody knows that is for the new antena nd new Data LTE speed.
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wify chip overheating
Wi Fi issue