iPhone: Siri, the iPhone's new voice-controlled assistant, not only lets you send messages and look stuff up on your phone, now you can also ask Siri to remind you of tasks via Remember the Milk.
You can, for example, tell Siri: "remind me to pick up the milk" and get that task added to your Remember The Milk to-do list.
To get this set up, RTM's blog says to go to your Mail, Contacts and Calendar settings on the iPhone 4S. Then tap Add Account > Other > Add CalDav Account. Enter www.rememberthemilk.com in the server field, and your Remember The Milk login details where specified.
Then you can start ordering Siri to remind you about your tasks.
Add tasks with Siri [Remember The Milk]