Comcast just came out with an iPhone application[iTunes link]. This application lets you check your comcast.net email, sync your comcast address book with your iPhone's. The one feature that I am really interested in is to be able to listen to the voicemail from our comcast phone.
This adds one feature that I enjoyed with Vonage. With Vonage you could configure the voicemail system to email the voicemail audio file to an email address. This made it very easy to listen to voicemail messages, while not at home. This iPhone application lets you listen to voicemails.
One feature that I would love to see is this application use Apple's push notification to deliver notifications of new voicemails.