Bryson Meunier posted a characteristics of the top 100 mobile search queries at AT&T. The top five keywords, in order, are "google," "yahoo," "sports," "facebook," and "myspace."
Further, Bryson says that mobile users are looking for navigational options as opposed to the traditional sit-at-your-computer search where you may not know what you're looking for.
According to the classification, the mobile queries were overwhelmingly navigational in nature, with almost three quarters of the queries coming from users who already knew what they were looking for: query intent percent of queries informational 12% navigational 73% transactional 15%
The article concludes with some best practices, including:
Using navigational queries such as branded terms, competitor terms and names of known products as core keywords could lead to increased visibility in mobile search engines.
...[U]sers are looking for usable sites, [so] developing a mobile web site and including the term "mobile" in the copy as a secondary keyword could lead to increased visibility in mobile search engines.
The research is very detailed and incredibly in-depth. If you're going along the mobile route, it's a definite read for you.
Forum discussion continues at Sphinn.