Thanks for the feedback!
A phone number is a lot more personal and immediate than email. We intend for this to be used with your most valuable customers, where you want to give them a direct line to someone senior at the company.
We started with Slack since it's an easy way to get your team on board without them having to adopt a new tool. We've already started speccing out a web-based tool to handle more complicated triage tasks.
The point on marketing message is appreciated. FounderPhone has worked well for us and our customers right now, and we think it can work for keeping account managers or founders close to their VIP customers, where you really want to be on top of any of their issues. We'll think about how to message that more carefully.