First, a couple clarifiers... ATSC = off air HDTV. If you want SD, you also need a NTSC tuner - and you have to check whether that's for cable, antenna or both. Finally, for digital cable you're going to need a QAM tuner, which will work with both SD and HD formats if it'sa HDTV tuner to start with. However QAM is available unscrambled and scrambled - for scrambled you MUST purchase a tuner with a cable card and you'll have to rent the actual cable card from the cable company plus pay for programming.

With that said, the Sony I have does all of this: HD, SD, off-air, cable, QAM, cable card.

I believe in the US most cable companies provide the local HD networks (CBS, NBC, ABC, Fox) unscrambled, and if that's the case you'd be able to tune them without further expense.