The initial backup should take care of you BBM contacts, however to be safe you have two more options. The first option is to backup your files locally llike to an SD card on your device. To do this perform the following:
- In the BBM, display the menu, and click Options.
- In the Contact List section, select Back Up.
- Select Back up files locally.
- Change the Save backup files to field to Device or Media Card.
- Click Back Up Now.
Noe the second method I know works with newer version of BBM, and that is to backup remotely via a registered email address. This option should be located in the same section as the local backup options. So you have a few options.