Not sure why it happens but sometimes after leaving my apartment where I have wifi on, I notice that the Internet on my 4S isn't working. I try turning mobile data off then on and also tried turning airplane mode on then off but neither work. Turning off the phone seems to get it to work but that's too much of a hassle having to do. I tried replacing my sim card but that didn't work. What should I do? Anyone have this problem? Only solution I can think of is a restore or contacting Apple for a replacement.