It is not necessary to install Apple Modem Updater 1.3.5 on the PowerBook G3 Series (Bronze keyboard).
The Apple Modem Updater was posted before the release of the PowerBook G3 Series (Bronze keyboard). It is intended for installation on original PowerBook G3 Series computers. When the PowerBook G3 Series (Bronze keyboard) was released, it included all the latest modem software.
Note: Macintosh PowerBook G3 Series computers should not be confused with Macintosh PowerBook G3 computers. Though the names are similar, there are significant differences. For more information differentiating between the computers, refer to article 24604: "
PowerBook G3 & G3 Series: Identifying Different Models"