As someone on the founding team of an identical startup a year ago, I can share experience:
- This market is beyond saturated, with countless large companies competing.
- In our experience, small businesses, teachers, etc. will do everything they can to avoid paying for the service, no matter how much value it creates for them. This is why many of the other providers have an 'ad-supported' free plan - freemium is a tough route here (but I'm sure they're just doing that right now as a ploy).
- The general consensus received is 'Oh we have [Facebook|Twitter|Email|...] for that, and they're all free!'
- SMS is more of a private sanctity that people use for family and friends. Facebook, Twitter, Email can be ignored, filtered using labels and lists, and checked when the person has time. People do not want to be SMS spammed with 'We have freshly baked cakes!' 5 times a day.