Ok The freezer trick worked for me and my Iphone 4s.
Wifi button was not greyed out but when turned on the wifi would search for like a second or two and find nothing. Also no wifi icon on main screen.
20 mins in the freezer at -18c brought it out and no power, connect to charger and wait for phone to start up and wifi now working again
Obviously this is more of a workaround than a fix but will wait and see how long it lasts.
Incidentally I too changed the wifi antenna on the top right hand side of the main board first as I thought it may have been faulty but obviously this is somthing else