Hello everybody- This thing can happend when you open your iPhone 4S, change the LCD screen or change battery. For me- as I work with iphones the solution what has helped me is simple- first of all go to settins- reset- reset network settings.. Your phone then resets all network settings and 90% of the time your signal comes back as it was! :) Remember that resetting all network settings will delete your wifi passwords as well- so you need to connect again in every place you have joined wifi. Hope this will help many iPhone owners! :)