If it's from BB to BB, you can use desktop manager. On the main screen choose Backup/Restore. Then click the Advanced button, and all the databases on your phone will load up on the right-hand side. Highlight the Address Book database(s) and click the "<<" button to temporarily store them on your computer. Then you can connect your other phone, make sure the database(s) are highlighted in the left column, and click the ">>" button. It may or may not prompt you to overwrite the current data.
