I want to implement a sort of CRM (Customer Relationship Management) web-based application, that is targeted for small businesses (small clinics, fitness center

I want to implement a sort of CRM (Customer Relationship Management) web-based application, that is targeted for small businesses (small clinics, fitness centers, motels, restaurants etc). The feature list is simple: 1. Adding/Removing customers and info on them. 2. Creating events for customers and employees and tracking these events. 3. Sending reminders for these events via SMS or email. 4. An easy web-interface for customers, which allows them to reschedule or cancel the event. The subscription would be free for managing ~20 clients and, I guess, starting from $10 when you want to track more than 20. Now I know about 37signals' 'Highrise' but it seemed to me more contact-oriented and much less client-oriented: good for business where you speak a lot to your clients and remember them better, but not good enough for mass-clients world. So, what do you think about it? Is it worth working on? Do you think people will pay for it? Would also be nice to listen to someone from Russia, if there's anyone here.