In fact, it is as easy as just say it. Under the JDS3 desktop
environment and running on Solaris 10+ (at least), you just have to
populate your ${HOME}/.fonts directory with your TrueType fonts (which
generally ends with a .ttf extension name) and log in again. Et voila:
any GNOME/GTK software will be able to use them automatically.
There no need anymore to use other X Window System tools, such as
xset(1) or mkfontdir(1).