SharePoint has the ability to send SMS messages to cell phones using a connector named Office Message Service (OMS). When an alert is fired, SharePoint can send an SMS message instead of an e-mail. This is decided upon by the person setting the alert.

Using OMS is just a suggestion though, as most of the actual development work has already been done. We just need to configure it and it'll run. The underlying framework is in place where we could replace it with a solution, such as Twilio (http://www.twilio.com/) instead. Although all of these systems have costs associated with them, the development teams working on the SharePoint system may have experience with one of these other messaging systems. That is a good reason to go with an alternative solution, such as Twilio.