Fring has an updated version of their popular VOIP app for the iPhone. The new version of Fring for iPhone 3.0 brings you Push Notifications.
How does the Fring Push Notifications work?
Whenever someone calls/chats you, you’ll receive a beep sound, as well as a pop-up window, telling you that your friend is trying to contact you. Once you click on that pop-up window, it’ll log you back into fring and take you straight to the relevant window.
While multitasking and background processes are not yet permitted by Apple, Push notifications adds some comfort to us. iPhone 2.x users can use always on to remain online. And with 3G unrestrictor you can also use Fring over your 3G network. And you must see that Fring Push video below 
iPhone / iPod touch downloads
{ 1 comment… read it below or add one }
This feature was already there in 1.1.4..
you can simply use backgrounder and set keep awake as green on Sbsettings and use it..
But Im glad its not officially available