While not documented, it is possible to activate remote SSH access to an ESXi 4.0 (free or paid license).

You need console access to the machine to turn on SSH access; it cannot be done with the vSphere client.

At the console, press Alt+F1 to switch to the console. You will not see a prompt, but you will be able to type in the logon name.

Type in unsupported then press Enter; you will see a Password: prompt. If you did not set a password in ESXi, type in unsupported. If a password was set for the root account, type in that password.

Once logged in, navigate to /etc, and open the file inetd.conf.

~ # cd /etc/etc # vi inetd.conf

In the file, find and uncomment the line(s) f  ...