Replying to Iphone Help? +karma

i jut got an iphone ( not 3gs just 3g) and i cant put music on it from 2 different computer and i was able to put music on my ipod touch from 2 different computers just by clicking "mange music manually" and i would be able to drag and drop without songs being removed. when i try to do that with my iphone, it says " to do this you must erase and sync you iphone to this computer, and all your other music and video will be earased" so basically it will only let me put music on from one computer.

limewire and frostwire dont work on one of my comnputers which is why.

+++ karma for help