Is it reconnecting shortly after you wake it up? As far as I know, all iPhones shut off the Wi-Fi radio in sleep mode after a certain amount of time. I know that mine does this, but it reconnects to Wi-Fi once I wake it up.
Thanks for taking the time to contact us. We will do all we can do to get your 4S to stay connected to WiFi. This is a feature that is very important.
First, I want you go to to Settings>WiFi>Select your WiFi network and tap the blue circle>Forget the network.
Secondly, go ahead and go back to WiFi to add the WiFi network & attempt the connection again.
Have you reset the network settings and attempted to connect to the WiFi again? http://bit.ly/QCxrjH.
Please feel free to let me know how the iPhone 4S is working once these steps are completed.
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I have a similar problem but mine is that the wifi just wont stay connected at my home. I tried the troubleshooting option posted on 9/24/12 by Tamara H at VZW but that did not resolve it. We have 2 other Iphone users in the house and their phones do not have the same problem so I believe it must have to be the settings on my particular phone. When I am at work or anywhere else that there is wifi I stay connected. It simply is my phone on my own home network.
Any other settings to try to resolve the issue?