This was driving me up the wall for some time.
One of my clients commissioned me to create a new NAS and move all the contents of the shared folders to the NAS.
All done with the wonderful help of FreeNAS (I suggest you read John Simmons' articles on FreeNAS).
I figured the easiest thing for me to do was to initiate the copy from the FreeNAS console.
A standard mount can be done with:
$ mount_smbfs
But this was failing and it was obvious that the reason was because of the domain. Didn't cross my mind to RTFM, so man
mount_smbfs
and lo and behold! An answer!
The correct way of mounting a DOMAIN share from the CLI is to add the -W [Workgroup] switch.
$ mount_smbfs -W [domain name]
(W not w. *nix is case sensitive)
A working example:
$ mount_smbfs -W mydomain.com
I was asked for my password and then voila!
The universe was at balance once more :)