In order to send text messages from Matrix you'll need to know your client's phone provider and that provider's email-to-text format.  The easiest way to do this is to have your client send a text message to your email address (not text-to-text or email-to-email).  From within their preferred messaging app, they'll send a message to your email.  When you receive this email, the "from" address should look something like:

[email protected] 

You can then add this email address to their contact record in Matrix (as their only address, or in addition to a traditional email address).  From that point on you only have to "email" your client for a text message to appear on their phone.  That message will still be from your email address however, it will not be a text message from you.  This means that any replies to this message will arrive in your email inbox just like any other reply to a Matrix message.

In addition to this, Matrix emails as well as most email providers support HTML code in the email (this is what allows you to have links and pictures in your signature).  Standard SMS text messaging does not support HTML, so the messages will be sent to your client with only the text of the message displayed.  Links will also be separated from the text, so "Click here to view listings" will now be followed by the link address (http://carolinamls.matrix.com/email/lisitngs/.....).  This means that the text messages your clients receive will not be as "clean" as the same message arriving to them in an email.  Links will still be fully functional, and will still take your clients to the appropriate listings on their Portal.