My iPhone 4S won't stay connected to wi-fi?

I have no password on my Internet at home and I have perfect signal. But when I click the button that turns off the screen, it goes to 3G and doesn't re-connect. Anything that I can do?

Try rebooting your Wi-Fi modem.
this happened to me once so I restarted it and then It connected again.

Hope this helps.

Well, Its apple's diabolical plan for 4S user to upgrade to iPhone 5

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