Add Calendar Functionality to Cpanel Mail Server?

We're using Cpanel to host a website and a mail server and we want to add group/shared calendar functionality? To access our email accounts some of us are using Outlook and some people are probably using iMail or whatever mac people use. And I was asked to see if we could add calendar functionality. The way it was described was so that e.g. when a person added their email account to their iphone then it should also come with a calendar.. Or like how gmail has calendars that come with it. I know very little about web programming /website /mail management stuff so not sure how the calendar + mail integration and stuff even works.. Looking into something called CalDAV at the moment..? Am I on the right track? Is there easy to use/install calendar software out there that you can just put on a cpanel server? Can any of the calendars on the following site be run of a Cpanel server? /http://www.linux.com/learn/tutorials/402382-the-five-best-open-source-calendar-servers-for-linux I'm also looking at Google Calendar as well and Google apps? But google calendar requires other users to have a google account which defeats the point of having a calendar for our domain anyway? I thought I'd ask here in the hope that some of you who run websites or manage web and mail servers for student groups/companies.etc. would explain how this stuff works /help /point me in the right direction? Thanks for your help! :) It's much appreciated! :)