Neat product, we rolled something similar to this using Slack where we manage the phone system, etc. I especially like how you can reply within Slack and text back the customer. Seems like your major problem with this startup is usage costs as text messages and phone calls can quickly add up. We are a small team of ~7 people and our monthly Twilio expense is twice your price here. I.e., not priced high enough.

I might prefer this product with a slight change: instead of trusting you my business phone number, maybe I could simply point my Twilio endpoint to your servers? That way you are not soaking up passthrough costs of customer usage; plus, I don't have to worry about getting my number from you after all my customers are familiar with that number. Anyways, it's a neat concept. I have provided our phone system to other businesses and can totally see the value in this product.