In order to send an SMS from your company's main number, the person logged into Workflow Builder must be designated the Operator for their account. This is done in the RingCentral Admin Console. Follow these steps.
- Log into the Admin Console.
- Click the "Phone System" tab.
- Click "General Settings" under "Auto-Receptionist."
- Expand the "Call handling", then click "Settings" tab
- Scroll down to "Call / Fax / SMS Recipients" and select your extension as the "Operator Extension." It is extension 101 by default.

Once you know the extension associated with your main company number or Operator, an administrator can load that extension into Workflow Builder. They can then build and design workflows on behalf of the Operator.