Why won't my iphone4 connect to my home wifi?

If you have truly tried EVERYTHING then there is nothing that can be done for you. Tell us what you have tried and maybe we can think of something that is not included in Everything.

As a start turn off or unplug your router for about 15 seconds to restart the DHCP server in it.

I don't know if this will help, but maybe it will. I had a weird problem that was a little different six months ago: https://discussions.apple.com/thread/3484296 . I turned off my router and turned it back on and that seemed to fix the phone issues both inside and outside of my home.

Tonight suddenly I had an issue where my phone decided it didn't want to connect to my home wifi anymore (phone just sat on 3G, and got a spinning wheel when trying to connect to my wifi network). My two laptops were both connected to the same wifi network, so it wasn't a network issue. In any case, I tried resetting network settings on my phone and that didn't work. So I turned off my router and turned it back on, and in a minute or two, my iphone connected itself to the wifi network.

Have you tried resetting your home router, and seeing if that gives your phone enough of a kick that it starts working properly again there and other places? Sounds weird, but it seemed to work for me for whatever reason.

This is not an iPhone issue. Many routers are unstable, and, after a while, will stop issuing new IP addresses. If a device is already connected and has its IP address this isn't usually immediately noticeable. But a device that either doesn't have an IP address or whose "lease" has expired tries to connect it does not get assigned an IP address by the router. Resetting or rebooting the router fixes it until the DHCP daemon that assigns IP addresses in the router crashes again. As the iPhone is only intermittently connected it is frequently requesting an IP address, so the router failure is more noticeable on iPhones.