Hello David
This is not a stupid question at all, and is a very valid use case. A lot of our customers are using our open platform, and integrating with 3rd party services for the use case you mentioned.
So short answer is that Yes, RingCentral supports it. All details on our developer platform and specifically SMS can be found here:
Getting Started: https://developers.ringcentral.com/guide/getting-started
SMS Developer Guide: https://developers.ringcentral.com/guide/messaging/sms/sending-sms
API reference: https://developers.ringcentral.com/api-reference/SMS/createSMSMessage
You can use your RingCentral account(i.e. same credentials) and login to https://developers.ringcentral.com/ and access even use API reference to try it out with your phone number. Let us know how it went.
Regards
Gurpreet Singh
PM, RingCentral Platform Products.