To ensure that your phone number does not unintentionally become unreachable, there are some restrictions on editing and deleting destinations from the address book.

You can only delete destinations from the address book if they are not in use.

If you still want to delete a destination that is in use, first assign another destination to your phone number or the extension currently using the destination. You can then safely delete the destination in question.

If a destination is in use, you can still change the name of that destination.

If you want to change the number of a destination that is in use, first assign another destination to the phone number or the extension currently using the destination.

You can then safely change the number of the destination in question or delete the destination from your address book.