Having recently switched to Ubuntu 8.10 Intrepid, I was puzzled to note that tftp client was not working from the command-line.
After filing a bug on launchpad, I became aware (thanks to Andreas Olsson) that there is netkit-tftp (what I had installed) and OpenBSD tftp,
which can found in the package tftp-hpa. So, if you need command-line ftp, just sudo apt-get-install tftp-hda.
Note that Windows command-line client syntax is different from Linux
tftp -i <x.x.x.x> put source destination
translates on the Linux client to:
tftp -m binary <x.x.x.x> -c put souce destination
where source and destination files are the required filenames.
-m binary replaces -i
-c put replaces put