You could put SMS and Voice on the same line, I have done that before. In regards to the Agent you could have it handle the calls then route for the Main Business Number or even use N8N/Make to route the calls based on caller ID from 1 central line with a transfer on the Twilio side of things, for Voice you can provide your own webhook on N8N/Make and then route to AI or Live based on caller ID, etc. just some ideas there hope they help