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.
Thanks in advance