Prior to Voxbone joining Bandwidth.com they were a provider we had chosen to avoid.
Voxbeam and Anveo Direct are solid choices for international DIDs.
Bandwidth.com has a poor reputation FYI, they pissed off a few Public Utility Commissions and were blacklisted from getting new phone numbers in some states.
We are looking for such a solution combined with data available via a Google datastudio connector. Could be an awesome feature to attract agencies as customers, who need to report to their clients.
I think that you are at least 20 years late for building a real domain business. I have been into in that game for more than 15 years and yes, it is fun, but it's not a (profitable) business. And if you want to make it profitable, it's not even close to a sidebusiness.
The front-end is built in React. The service is deployed as a single Spring Boot application written in Kotlin. In terms of workflows, there is state machine that jobs process through (asynchronously with persistent state) within the service itself. It depends on no external workflow engines.
Infrastructure components include CosmosDB, Azure Blob Storage. The service is deployed as an App Service.
The STT and Search tech I'll keep under-wraps for now as they may change.
Thank you very much for sharing your experience with HN. From my own point of view (as the CEO of a performance marketing agency working with Google Ads & clients budgets daily) I have to add, that this are learnings your agency should have protected you from.
Showing the bot something different than the user could be seen as cloaking. We also do that in some cases. Just be really carefull with that strategy.
Depending on the product, i would suggest option 1 or 3. Maybe you can find a limitation for the free (lifetime) version, where the free users can help you to get some traction. (Like trello.com does)