Email Hosting vs. Exchange 2000 Server

Hi everyone,
We are currently working on bringing in Exchange server 2000 for the benefits of Scheduling, Calendaring, and collaboration features. We currently have a web hosting host our pop3 email addresses for all of our user (about 75 users)and we don’t know what the pros and cons are to bringing the email hosting in house. We have a t-1 line as our internet connection.