WiFi Connection Issues with iOS4

I have a jailbroken 3Gs that had 3.1.3 that had no problems connecting to my wireless access.

I installed the iOS4 on it and most times I am unable to connect to or stay connected to network.

I purchased the iPhone 4 and am having the same problems.

I have shut down the router, reinstalled the firmware on the router, powered down the phones and the connection problems continue.
Both devices have a case so I don't believe it's the same issue as the bars.

I am using WPA2.

Not sure what else to do.

Suggestions please.

Thanks in advance

go into settings > reset

and reset the network settings. Then perform a reboot.

rest everything