может что и лишнее:-) но работает!!!
id nagios
uid=181(nagios) gid=181(nagios) groups=181(nagios),0(wheel),66(uucp),68(dialer)

копай в сторону:
ls -l /dev/cuau0
crw-rw----  1 uucp  dialer    0,  39  3 фев 19:18 /dev/cuau0

вот пример:
grep sms ./commands.cfg
       command_name                             notify-host-by-smsclient
       command_line                             sudo -u uucp /usr/local/bin/sendsms $CONTACTPAGER$ "$NOTIFICATIONTYPE$: $HOSTADDRESS$ $HOSTALIAS$ is $HOSTSTATE$ Time: $LONGDATETIME$"
       command_name                             notify-sevices-by-smsclient
       command_line                             sudo -u uucp /usr/local/bin/sendsms $CONTACTPAGER$ "$NOTIFICATIONTYPE$: $HOSTADDRESS$ $HOSTALIAS$: $SERVICEDESC$ is $SERVICESTATE$ Time: $LONGDATETIME$"