Google was granted a patent (# 7,027,987) today that covers converting voice to search queries. While there is not currently a mobile version of the technology, it seems like the most obvious extension for the technology. Google’s technology converts natural spoken language into a boolean search query. From the patent’s abstract:
The system receives a voice search query from a user, derives one or more recognition hypotheses, each being associated with a weight, from the voice search query, and constructs a weighted boolean query using the recognition hypotheses. The system then provides the weighted boolean query to a search system and provides the results of the search system to a user.
There are several players in voice-to-text (VoiceSignal) and voice search (V-Enable, Promtu) in the mobile space. Google is the only major search engine to publicly test a voice interface.