I came across an interesting post by Gregg Stewart on Search Engine Watch last Oct. 12. The growth of directory assistance (DA) services has spawned a new a new sub-category: voice search.

According to Stewart, voice search enables users to access name-based information and/or category-based listings in much the same way as printed White and Yellow Pages, all supported via advertiser sponsorship as opposed to user charges.

There have been a number of these offerings over the years (HelloYellow, 800-411-Metro, etc.), but to date, none were successful at attracting user and advertiser acceptance, the article stated. With today’s mobile-enabled consumer, however, we’ve crossed the first hurdle. We now have users. Lots of them.

The Kelsey Group estimates there will be nearly 270 million calls in 2007 to ad-sponsored/free DA, the vast majority from mobile users. From now until 2012, ad sponsored DA is expected to have a 50 percent compounded annual growth rate and will be the leading DA source by 2012.

Even now, a few companies have already fielded products to attract users and establish a market share. Some of these large players include Jingle Networks (Free411), AT&T (800YellowPages), and even Google with their own GOOG-411.

These providers have a similar offering: users access listings for a category and are then required to listen to a brief, 15-second audio ad from the advertiser before receiving the request information/listing.

Voice search, while not a new concept, is beginning to see a perfect storm of opportunity; users are lining up because of mobile search needs, advertisers are seeking new measurable manners of gaining sales leads, and there’s backing by major brands such as Google and AT&T, Stewart writes. While many mobile opportunities are still in the distant future, voice search represents an opportunity in the here and now.