Notifying user’s with text messages.
Nagios can send text messages on respective mobile no. via sending mail to respective mobile carriers.
Mobile no. can be defined for every user and Nagios will send alerts to xxxx@mobile_carrier.yyy where xxx is the mobiel number.
A detailed description can be found on Nagios website -
https://assets.nagios.com/downloads/nagiosxi/docs/How-to-Setup-SMS-Alerts-In-Nagios-XI.pdf