I've not seen said marketing campaign, unless you mean the ads where they happen to mention it as one of half a dozen or so features. And it's not as if marketing doesn't to sell people on things they don't need.
If it really was such a big deal as you suggest, I doubt VZW would have more subscribers than anyone else.
I do know that people talking in a forum don't represent the user community as a whole, but rather a subgroup.
As yet, I'm not finding survey results that show it's a popular feature.
Have you lived under a rock for the past 4 years? The ads with Luke Wilson where the other guy had two phones so he could talk and web? The ad with the guy at the office working late whose wife calls about their anniversary dinner? These ads are EVERYWHERE and have been for years.
If you haven't noticed those ridiculously carpet-bombed ads, it's not surprising to me that you haven't noticed people talking while using their iPhones for other things.