You can send SMS messages to the members who have opted into this from their profiles!
On the member profile, by clicking Settings > Text Messaging, your clients can request the verification code to be sent to the number they provide. Once they enter the verification code, they will be able to receive the SMS messages you send from the Triib Admin.
To send out a text, simply click Messaging > Compose Text Message! This will allow you to draft your message and select the recipients.