In the past I would just use my iPhone's email-to-txt email address. However, when I received the txt message, it wasn't formated very pretty, and it would have a different "From Number." So if we had a crazy day, I would have 20-30 message threads in my iPhone all about Nagios. [...] What I like out this setup is with Twilio, I can buy a phone number for $1 a month. So all my notifications come through the same number.
He's included the PHP code he uses to send the notifications (using the Twillo library) and the Nagios commands he configured to send the notifications to that script via the command line.