Chpwn has developed and released Zephyr, a jailbreak tweak in cydia to enable multitasking gestures on iPhone and iPod touch. Zephyr encapsulates capabilities similar to iPad on iOS 5. Check out the demo video of Zephyr working on iPhone.
Zephr basically works in two ways, you can swipe from the bottom to see multitasking switcher from anywhere from your iPhone and you can switch to different application by swiping left or right from the edge.
From swiping up to show the multitasking switcher or quickly swiping to a different app, Zephyr is all you need to quickly and easily control multitasking.
Zephyr is available in cydia for $2.99 and runs on jailbroken devcies running iOS 5 or later. To install Zephyr, you just need a iPhone / iPod touch running and jailbroken on iOS 5.0.1 which you can do easily with redsn0w 0.9.10b2. Once jailbroken, just open cydia and search for Zephyr in BigBoss repository and install it.