External companies sending SMS on our behalf

We use 3rdy party companies to send text to customers for most of our text messaging. Our employees communicate with the customers through the websites of these companies. We do use RingCentral for texting as well, just not nearly as much. I realize I will have to setup TCR for our use with RingCentral. My question is about these 3rd party companies. Are we responsible for setting them up in TCR as well, or is that something the are responsible for? I'm not sure how to approach this since it's not through RingCentral, but they are sending them on behalf of our company.