How to add line numbers to VI by default

I am running on Snow Leopard 10.6.6. at the time of this post.  VI is a handy tool to use because it is installed on every single non-windows box I have ever seen.  I originally only used nano and I have found out that nano is not everywhere.

1) you need to locate your .vimrc file, on osx I just did a locate vimrc and got this

bash-3.2# locate vimrc
/opt/local/var/macports/sources/rsync.macports.org/release/ports/editors/vim-app/files/gvimrc
/opt/local/var/macports/sources/rsync.macports.org/release/ports/editors/vim-app/files/vimrc
/usr/share/vim/vim72/gvimrc_example.vim
/usr/share/vim/vim72/vimrc_example.vim
/usr/share/vim/vimrc

2) now just vi open that file

I did a vi /usr/share/vim/vimrc and then added the line set number to the end here is how my file looks->

" Configuration file for vim 
set modelines=0         " CVE-2007-2438

" Normally we use vim-extensions. If you want true vi-compatibility
" remove change the following statements
set nocompatible        " Use Vim defaults instead of 100% vi compatibility
set backspace=2         " more powerful backspacing

" Don't write backup file if vim is being called by "crontab -e" 
au BufWrite /private/tmp/crontab.* set nowritebackup
" Don't write backup file if vim is being called by "chpass"
au BufWrite /private/etc/pw.* set nowritebackup

set number

3) now quit and save, everytime you open vi it will show line numbers, to turn them off you can do a :set nonumber