I have a quick question if anyone can help

It was my ipod touch but i dont want this happening to my iphone

What happens if the computer the itunes is on breaks down and you have to formatt it and install itunes

I did the authorise thing and when i synced it, it deleted all my music and apps etc

If say i have my iphone with loads stuff on it and the laptop needs formatted, how do i transfer it from iphone to computer without it deleting it?