iPhone app - What does the SMS icon do on a coworkers name?

When logged into your app and looking at the roster for the day, you can select a coworkers name and 4 different contact method icons will appear.

The second icon is for SMS messaging.

When selecting this, you will be brought out of the application and directly into your text messages with a blank text started to the selected coworker. Standard texting rates apply.

If this icon is grayed out, your coworker does not have text messaging enabled for their account.