@DAVID CONROY , You can create a non profit brand and chose a low volume conversational campaign time for this use case.
Check this link: https://support.ringcentral.com/article-v2/Setting-up-TCR-registration-assigning-numbers-to-SMS-campaigns.html?brand=RingCentral&product=MVP&language=en_US
For opt in consent, yes it's needed even for 1-1 conversations, but it's not as strict as a marketing messaging consent. So for your case, as mentioned in above article, it may fit in"
Initiating the text message exchange in which the Message Sender replies to the Consumer only with responsive information." You can provide details on who initiates the message and if it's your customer, that it's kind of implicit consent. If your office starts a SMS normally, then yes you need to document the consent of the recipient.
Regards
Gurpreet Singh
GPM, RingCentral Inc.