Hi @TechSmith77 , thank you for posting in the Q&A forum.
When we use the OOB SMS function via Central Administration > System Settings > Configure Mobile Account under "E-Mail and Text Messages (SMS)", we get to use Text Messages (SMS) as an additional "Delivery Method" when using Alert/Notification feature.
SharePoint does not support using mobile number as an authentication method or integrating with lists/libraries using SMS system. You might find related function using third-party solutions instead.
Here are some references on this topic: Configure SMS Alert On SharePoint 2013. / Send SMS messages from SharePoint.
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