You can check most any kind of email account with Windows Mobile. However, it syncs PIM data (contacts, calendar, tasks) with Outlook on the desktop and Exchange server (also Lotus Notes and a few other business systems) but not web-based email services. I believe the older 2.0 version of Yahoo Go could handle syncing to Windows Mobile. I hear they removed the contacts backup feature from version 3. For syncing to Comcast, I have no idea unless you can download the address book into Outlook.
-------------------- Lisa Gade Editor in Chief, MobileTechReview