I am not a super experienced C# user, though I have some experience in .Net and VB.Net. Just got this new job and my first assignment is a mission critical part of the business. It is pretty important I get it right so I was hoping for some sage advice.

We have created a calendar using jQuery, C#, .Net & SQL Server 08. The calendar works but now we are wanting to add email, SMS and voice-call reminders. We are a small company and can do whatever we need to do with no restrictions on our IT environment. I have some base-line experience with Unix servers but would prefer to stay in the Micro$oft universe if it is prudent to do so.

I know how to add the API calls and services to initiate these reminders (using built in email services for email and Twilio.com for SMS). I am asking for advice about how to approach a reliable and timely listener service that knows when to call the service or API for the reminder before an appointment. EG. SMS: "You have a conference call in 30 minutes."

I have done some research, but it is hard to know what is a proven reliable approach. What I am looking for is an experienced opinion on a good (or the best) strategy for implementing a solution that will reliably listen for appointments and dispatch the reminders when needed.