Comcast offers a free Comcast Mobile app for iPhone/iPod touch devices. It offers access to your Comcast services and version 2.0 includes remote DVR functionality, as well as other new features.
Now Comcast has a new video out today demonstrating its new version of the app, including the remote DVR function. You can find it at http://blog.comcast.com/2010/03/comcast-mobile-20-now-available-on-the-app-store.html. And you can find the app itself at the Apple App Store (http://www.itunes.com/appstore/).