@golfcave- The main difference is that with High Volume SMS, you can access batch API (https://developers.ringcentral.com/api-reference/High-Volume-SMS/createA2PSMS) and HVSMS also manages Opt out list for the customer. However, HV SMS doesn't support MMS or access via MVP app.
Having said that, most of our customers use cases can be full-filled by Enhanced Business SMS, which is our standard solution. Also, in near future we are planning to bring HV SMS to Enhanced Business SMS, and just have one SMS solution with all features.
So my suggestion is that if you need access to batch SMS API or have to send >50K SMSes per day, then use High Volume SMS.
Other wise use Enhanced business SMS, and you can use MVP App(https://app.ringcentral.com/) for conversations, https://sms-campaigns.com/ for sending SMS campaigns and EB SMS APIs(https://developers.ringcentral.com/api-reference/SMS/createSMSMessage) for any API based integrations.
Regards
Gurpreet Singh
GPM, RingCentral Inc.
