Analyzing the mobile search and content discovery space as I have for the past several years I recall the key message of a worthwhile white paper from SEO firm OneUpWeb (reg.req): mobile search has delivers the strongest value proposition when users are in buy-mode. That’s the point when passion and purpose cross, and users need to know. Clever providers are borrowing a page from this strategy. Newest to the fold is Sprint Nextel, which today has taken the wraps of a combination mobile search and GPS service, the WSJ reports. Such services are not new, but this one – called Slifter—overcomes a huge usability barrier since it lets users locate products in stores without having to know their ZIP code.

Slifter, which is offered by GPShopper LLC, is delivered as a downloadable app at a cost of $1.99 a month for Sprint subscribers with data plans. The service lets users do more than locate goods; they can save items to a shopping list, which they can share with friends via SMS. The company is reported as saying that Slifter has been used by several hundred thousand people, most of whom learned of the service from friends through Slifter’s sharing feature. The service draws from an index of 65 million products at 30,000 store locations (mostly the big U.S. chains). The business model is stable enough – “retailers provide the data to GPShopper and pay the New York start-up a fee whenever consumers click on a link to one of their product listings, much as advertisers pay search engines such as Google for clicks on keyword-based text advertisements.” (Wonder when Google will add a similar service to its local mobile search scheme. Then it would be in a prime to dominate the supply-chain – so to speak – from beginning to end…)

Update: Seems that I’m not the only one who sees a huge opportunity in services that sit at the intersection of mobile search and shopping. E-consultancy provides a look at the partnership between Vodafone U.K. and PriceRunner, a price comparison service,  and a worthwhile Q&A. The focus: price comparisons on the go. And it surely won’t be the last one…