In case you are using an older iPhone, you might well be versed with the fact that the phone does seem to have a certain amount of lag when using with iOS 4 and have plenty of applications running in the background. One solution. That was widely suggested is switching the multitasking off as it really does make a difference to the speed, but how to do that? The tweak that would help you is called z toggle and is available on Cydia.
Since this tweak is available on Cydia it is mandatory that your iPhone is jail broken and has the Cydia store installed. This tweak can also be applied on your iPad and iPod touch. The steps to get to tweak are rather simple and all you have to do is, go to the cydia store, and search for z toggle in the search bar and then install the tweak, restart the springboard and exit out of Cydia. Once you do that, you will see a new icon on our springboard of z toggle.
What this does is that it gives you various options for your devices. For example, you can switch on or off the desktop wallpaper or even the multi tasking of your device. This is certainly helpful in conserving battery and making your iPhone snappier than before. The tweak is available for free so go ahead and download it, in case you do not need either of these two features or feel your phone is Lagging.
Here is a video showing you how the tweak works.