installing apps from several itunes

[pixy]

Hi every body,
I want to know how i can install apps to my Iphone 4 from several computers and itunes, I saw a man that he can install apps to others iphone without Sync their iphone.
how can i do it??
TNX alot

 

[bab2010]

Using iTunes? It can't be, iTunes will erase all audios videos out from the phone before syncing with a new iTunes.