Here we go. Notice: this is for windows, you will need
1# WinSCP to SSH into your device, 2# plist Editor for windows
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1- jealbreak your iOS 4.3.1
2- in cydia download and install openSSH into your phone, restart your phone afterward.
3- download and install on your windows computer, WinSCP
4- # your phone and your computer have to be on the same wifi # Now open WinSCP and in
>>(section - host name) = input your iphone wifi ip address.
>>(port number) = 22
>>(user name) = root
>>(password) = alpine
Clik Login button.
5- a new window will open, navigate to system> library> CoreService> SpringBoard.app> N90AP.plist
6- copy N90AP.plist to your desktop then open plist Editor for windows, from the plist editor, open the N90AP.plist that you just copy to your desktop.
7- Scroll down to find the string multitasking, right under it create a new string multitasking-gestures and add the value true
8- save the changes, now drag and drop the N90AP.plist on your desktop to the SpringBoard.app folder. A pop up dialogue will ask to confirm overwriting the original with the one you are droping into that folder, click yes overwrite.
9- after that, disconect your device from your computer and restart your device, wait until the device load and screen goes to standby mode, then you can start using gestures multitasking on your device.
10- you can 4 fingers swipe up to revel multitask bar, 4 fingers swipe left or right to navigate between open apps, 5 fingers swip inzooming to close an opened app and get to the home screen.
Good luck.