Google has has a demo of voice-activated searches: Searchers call a Google supplied number, where a prompt asks them to "Say Your Search Words." After a minute, the results are returned and, in the demo, the searcher clicks a link that leads to them. In a real-world application, the results would presumably be sent to a mobile phone screen or in-car system. The obvious eventual application is for mobile phones. Mobile web services are on the rise, and mobile phone keyboards could make typing in keywords a nuisance.
One notes that since keyboards generally are a nuisance, voice commands for many input functions would be desirable.