MobileMe allows entry of Todos but they don't sync with Outlook nor with the iPhone. Perhaps if you have a Mac this may work but I don't have one so I don't know.
The iPhone has no built-in Task manager but there are many available in the AppStore. The solution for me was to stop using Outlook for task management and find something more robust. Here is my setup:
- iPhone: Appigo Todo
- Windows Desktop: none - see online
- Online: Toodledo
- iPhone: Built-in Calendar app
- Windows Desktop: Outlook 2007
- Online: MobileMe
MobileMe keeps my home computer's Outlook calendar in-sync over the air without me having to do anything special. Whatever I add/change/delete on the iPhone is auto-synced to my desktop and vice versa.
Toodledo does the same for Task Management except it doesn't use Outlook. It's an online system so you simply run it in a browser. Appigo Todo on the iPhone syncs automatically with it.
Note that you can sync both Appigo Todo and Toodledo with Outlook if you want to see your tasks there, but I don't because Outlook does not support sub-tasks (e.g. projects) and is missing a lot of other helpful features you might want to use for GTD (e.g. contexts).
Hope this helps.