vim binary is included in the software companion CD, you can either download it from sun
http://wwws.sun.com/software/solaris.../download.html
or download vim only packages from one of the freewares sites sunfreeware of blastwave.org.
Beware that with sunfreeware site, you also need to download all the prerequisite packages cited (gtk, glib, atk, pango, libiconv, ncurses packages and either the libgcc or gcc package).
Blastwave is far simpler to use: just download the pkg-get script, and then it will do all the dependancy job for you (pkg-get install vim)