Is there a reason that the generic Salesforce model makes phone calls "Tasks" and not "Events"? It seems like calls have start times and end times just like Events. What advantage does not having those fields give?
Actually, phone calls are Tasks and meetings etc. are Events. Then both are grouped as activities. It is essentially a very abstracted back end data model, presented in Salesforce as two tables, with common functionality.
The best place to start would probably be the Salesforce api docs for each, https://www.salesforce.com/us/developer/docs/api/Content/sforce_api_objects_task.htm (Task) and https://www.salesforce.com/us/developer/docs/api/Content/sforce_api_objects_event.htm (Event). Though if you google salesforce tasks and events, you will find a lot of posts and discussions about the best practices, experiences and tricks of these tables.