Can multiple iPhone's be synced?

Apple goes to great lengths to make sure things like what you’re describing, don’t happen. When you try to sync from someone else’s itunes library, itunes will erase all your existing media on the iphone before syncing.

So you’re saying one of us would lose our music, apps and everything?

Not apps. Music and movies, yes.

Wow—that is completely retarded.

It keeps the cost of your music down.

You can sync multiple iPhones to one computer with no problem. I think Heretic misread your question and is referring to you not being able to sync one iPhone to multiple computers for purposes of copying music and movies to a friend’s computer for example. But syncing multiple iPhones to one computer is no problem at all. They will both behave perfectly normally.

If you need more evidence: http://discussions.apple.com/thread.jspa?messageID=8439186

If the phone hasn’t been synced to that computer before, then what Heretic mentioned will happen. iTunes will remove the music before syncing the music on the computer. Apps shouldn’t be affected.

Has this phone ever been connected to a computer? If so, i suggest only connecting it to the original computer if possible.

Music and movies purchased on iTunes are linked to that account and available to download from the iTunes store BUT may be affected by DRM.