How to put songs to my iphone from itunes without deleting songs in my iphone

I have a problem. My friend placed music in my iphone using his laptop recently. Unfortunately i want to put more song in my iphone using my computer. However, I cant sync my iphone to my comuputer since it says that syncing will delete all the music in my iphone. How can i put music in my iphone without deLeting the songs in my iphone? :| :|

Solution 1:

You will need to manually manage your music now. You can do this by plugging your iPhone into your computer (or wifi connecting to iTunes), and then, after selecting your iPhone, under the "Summary" tab, select "Manually Manage Music and Videos".

If you are running iTunes 11 go to the the "On my iPhone" tab, and you can now manually manage the music that you have on your iPhone. Unfortunately, unless you erase the music he shared with you, you won't be able to automatically manage your music.