There's only one way and that's with the assistance of a B&O technician (or a savvy salesperson) and their service computer. They can store your phonebook as a backup and give it to you on a file. You can load it back onto your base if anything happens. However, I'm not sure if this can be done from one model/generation to another.
There is scarcely anything in this world that some man cannot make a little worse and sell a little more cheaply. The person who buys on price alone is this man's lawful prey. - John Ruskin