Zdnet reports a growing trend toward mobile search built on top of SMS. For example, 4Info is expected to announce a $7.5M funding round from US ventures. Google has its own SMS service as does Yahoo.

For me, mobile search on a rich device like the Blackberry is an absolutely compelling application. I still need to be convinced about the utility of T9 search on a device with a tiny screen. Let’s assume, though, that SMS search becomes compelling or enough people migrate to richer devices.

The key questions for companies in this space are the revenue model and competitive differentiation. I believe the thinking that has been applied to these questions has been overly constrained by past assumptions about desktop search.

An additional constraint, as always, has been the shortsighted greed of the carriers themselves. I like this quote from an O’Reilly article titled 2005 is Year of Local Mobile Search

The beauty of a application like Berry 411 is that it that allows me to encourage charitable contributions, provide a lot of value to many people with minimal effort, and focus purely on delivering a usable application while sidestepping all of the difficult questions of monetization.

I believe a lot of innovation in mobile devices will bubble up from the grassroots, as in the early days of PCs– if carriers and the data providers don’t kill it.