iPhone and Exchange Sync Question

Hi all my exchange server has failed so had to replace it which I have now done but im unsure about the phones. All the users phones still have the contacts and emails on but there Outlooks are effectly blank.

If I sync the phones will I loose all the info on the phone as it will sync with the blank mailbox or will it copy all the items from the phone to the mailbox?

Any help would be great.

Thanks