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.
~ # cd /etc /etc # vi inetd.conf
/etc # ps ax | grep inetd 40045896 40045896 busybox inetd /etc # kill 40045896
/etc # inetd /etc #
You can now test SSH access by logging in with your user and password you use with vSphere client. From here on out, you will be able to use SSH for a number of things (like SNMP monitoring, backup complete VMs, etc.)