Yesterday I upgraded to OS 4.2 and all my music are gone on my Iphone after upgrading. When i go to "Ipod" on my Iphone, the message is "no content, go to Itunes to download music" When i check the memory on my Iphone it says that i've got 1078 songs stored on the Iphone. How du i get my music back? Do i have to connect to my Mac Book pro again and download from the library there or can i "do something" on my Iphone? Thanks!
Same thing happened to me with my iPod touch; I also lost all videos and calendars in Outlook as well as all music. Luckily, as mentioned here, a simple sync restored everything. It's a pity that Apple doesn't warn users who have upgraded to OS4.2 about this so that we don't freak out.