After searching the internet for several hours for a solution to this problem, I thought it might be helpful for others if I posted my solution here.
My wife just bought an Incredible yesterday. She didn't have a Gmail account, so she set it up on the phone right after buying it. Under Settings, Accounts & sync, her Gmail account was listed but after selecting it there were only options to sync Gmail and contacts--calendar was missing.
I also have an Incredible so I could do a little troubleshooting. I could add her Gmail account as a secondary to my phone and it would allow me to sync with her calendar. Conversely, she could add my Gmail account to her phone and it would find my calendar.
Some of the work arounds online suggest creating another Gmail account and syncing with that and then sometimes it would allow the primary account to find its calendar. This did not work in my case.
After calling Verizon technical support and being transfered to an Android specialist, he thought the problem probably was that there was an issue with the syncing when the account was created. He recommended resetting the phone so that it could resync with the primary account. The primary account cannot be deleted and added again without a phone reset.
If this describes your problem, make sure you have your contacts and any app-specific data backed up. Go to Settings, SD & phone storage, Factory data reset, and then Reset phone & internal storage. Follow the directions that follow. Remember this erases all information on your phone (except what is on your micro SD card). Good luck!