Yes you should be able to sync your contacts on your Blackberry with the address book on your Comcast email. The best way to do this is to set up your Blackberry Desktop Manager to use your Comcast address book as your Blackberry address book. The instructions to do this are listed below:
1. Connect your BlackBerry® device to your computer.
2. Open the BlackBerry® Desktop Manager.
3. Click Synchronize.
4. In the left pane, click Configure > Synchronization.
5. Click Synchronization.
6. Select the Address Book check box.
7. Click Advanced.
8. On the Address Book tab, click Map Fields.
9. Complete the instructions on the screen.
10. Click OK.
Hope this helps.