While iPhone users can sync their can sync their calendars with Outlook or Google Calendar. Maintaining a task list on the iPhone presents a challenge in that there is no native task application on the device. ToodleDo offers a third-party alternative. From the reviews I have read, the program works well.
Here is a short video demonstrating this software:
The program is available in three versions: Free, Pro, and Pro Plus.
We all need a comprehensive system for staying on top of all of the commitments we have made to ourselves and others. For the iPhone user, this program may be a very good answer.