The point about having a fixed upfront cost/ceiling is valid. This is the reason why we have pricing plans with a fixed cost based on the customer's estimation

The point about having a fixed upfront cost/ceiling is valid. This is the reason why we have pricing plans with a fixed cost based on the customer's estimation of their usage. If you signup for a $19 plan, you will not be charged more than $19 per month. Companies are able to roughly estimate their monthly conversations based on the number of conversations they have in a day. After this estimation if the number of conversations exceed their monthly limit, we currently do not prevent the extra conversations or charge the customers more. We hope to have a open conversation with our customers who consistently exceed their limit and figure out the right model for the customer. The underlying philosophy about our pricing is, we want help our customers succeed by enabling their support and sales conversations, and not be a barrier ourselves.