To text from the phone system, you need to log into the online portal at portal.vistanet.tel

Next, click on Apps on the top menu of the screen to bring up the following dropdown. 

 

Click on WebPhone.  

In the bottom right corner, click on the red circle with the plus to bring up the following menu:

Select the Pencil button.    This will bring up a Search bar.  In the search bar, you can enter a 10 digit phone number. After you enter the phone number, it will bring up an option for SMS.  Select this, and then press the green checkmark(circled in red).  This will start the conversation window.

Now you can just type in your message and press enter to send.