Advertising Management Calendar

I would like to create a calendar system for my newsletter that would allow clients to sign in and add and edit their own advertisements that I would then copy and paste in on the day of publication....would like the calendar to also be able to send a reminder to the client on when the advertisement will be running and the deadline for changes. These will be simple text adds. They will go in one of four categories so there needs to be 4 spaces for each day on the calendar. There may be some simple plugin for wordpress that can accomplish this so if we need to setup a site using wordpress to accomplish this that is fine... or maybe you can think of a solution using Google Calendar ? Just let me know your bid and what you are thinking....