You can’y run more than one application on Iphone at a time Right? Wrong!
A new application called backgrounder allows you to run more than 1 apps in Iphone while the rest except one run in the background.
You can do this by downloading a file , and browsing the I-tunes store and whatever you want to run.
But like always every coin has two sides even this app has. This will drain your Iphone battery like anything and even leave you with very slow performance.

You cannot run 3 rd party applications with it i.e you cannot run those applications in the background which are not officially downloaded from the I-Tunes store.
If you still want to run a application in the background you can request the application producer so that he can edit the application and then make it usable with backgrounder.

Actually I recommend you using this Application if you use light application i.e which don not require much space and not  the applications which use applications which have huge size and take long time to start up and load because if you do so then you will end up getting your Iphone hanged again and again.

You can install iPhone Backgrounder via Cydia, the installer app for jailbreak iPhone apps
First you need to download Cydia and via that you can install Bacgrounder.