I found this method on another, excellent website. It explains how to export your address book from your BlackBerry into a .csv file that can be opened in an Excel spreadsheet, edited, and transferred back to your BlackBerry using the Desktop Manager. I've exported mine, edited it, but haven't had time to transfer it back to my phone. The web address is:
Managing Contacts in the Address Bookxxx8211;Using Excel « My BlackBerry Pearl 8130