An interesting article describing howto use Skype to send SMS notification for Nagios or op5 Monitor can be find here:
http://wiki.nagios.org/index.php/SkypeSmsNotification
My recommendation is to use an GSM modem to send SMS, because if the network is down no SMS can be sent with this solution and SMS is normally used as an alternative alarm route.
Another aspect is that Skype is using propertiary protocols and that should be avoided.
