I have not used Kannel, but a quick google search indicates that it provides a web/cgi script to send sms, so it should not be hard to configure fop2 to send sms through it. Here is a sample URL I found via google to send sms via web:

http://localhost:13013/cgi-bin/sendsms?username=xxxxx&password=xxxxx&to=$cellphone_number&text=$encmsg

Here is the line you should use in fop2.cfg to match the above:

sms_api_url=http://localhost:13013/cgi-bin/sendsms?username=xxxxx&password=xxxxx&text=${MESSAGE}&to=${NUMBER}

Best regards,