All my notes and calendar information is gone? How can I get the info back?
I presume the information is missing from your iPhone and not your computer?
When did you last perform a sync? If the information was on your iPhone at the time of your last sync it might be on your computer (as long as your iTunes was configured to do this).
If this is the case, perform a sync to copy that data back from your computer to your iPhone.
RTP.