recover WPA2 passphrase from iPhone4s or its backup?

I forgot the passphrase to a WiFi network but my phone still connects to it.

My old iPhone3 used to be connected there, then when I migrated to an iPhone4S the settings were magically transferred through iTunes. I guess the WPA2 key is therefore in the backups (which are not encrypted)

Is there a way to recover this WPA2 key from either the phone directly or from the backups? I read that there is an app for jailbroken phones but mine is not.

Thanks!

If you don't mind jailbreaking your phone, there's an app called “Wi-Fi Passwords” in Cydia that displays the Wi-Fi networks you've connected to and their passwords.