I don't use it for OTA, but yes, Both Tivo HD and the S3 can take ATSC input, which is what you're asking about. I have no idea if it will function without a service plan, and how the integration is with the OTA channels. You might want to head over to the tivo community forum and do some research there.
Both the Tivo HD and the S3 have esata ports, and you can expand the storage via plug-n-play with certain certified (Western Digital My DVR Expander) esata external drives, so don't worry about the space. Tivo HD will be fine, and in some cases maybe better than the older S3.
-David
Cool...Thank you David.
Due to your recommendation I paired a Tivo HD with the WD Drive which should give me twice the available storage space of the S3 for about the same price of a single S3. I just ordered it on Amazon for a hell of a price.
I'm certain I will have to pay now for a service plan. $299 for three years looks to be the best deal these days, although I may just buy a year for now to get a better sense of the unit. One REAL nice feature the old Reply unit offer's is the 30 second skip button. 4 - 6 presses and we're usually clear of most commercial breaks. I don't believe Tivo has this.