There are a lot of different ways that you can handle calendar and contacts. Right from the start you should be aware that we are primarily an email service and that using us for calendar and contacts will not be as simple as using Google or iCloud to manage email, calendar, and contacts on your devices. Those devices were built for those services, their implementations built into major software, for an easy UX that can only be provided by a company selling a product with the kind of adoption levels you would find with Apple and Google. If you want to continue to handle your contacts with Gmail, iCloud, Outlook, etc. this is fine and frankly what many of our customers do.