Hi,
Ensure that you have typed correctly including the prefix / at the beginning. Or depending on the Ubuntu version e.g. sudo service kannel start.
The other way to start kannel is to run:
bearerbox -v 1 /etc/kannel/kannel.conf
smsbox -v 1 /etc/kannel/kannel.conf
You can also edit the /etc/kannel/default and uncomment START_SMS = 1 to start at boot.
Regards
Thanks