People searching on the normal web version of Google are given a list of results matching their query. In a simple terms these results are ranked according to the number (and quality) of other websites that have voted for them using links.
In Google’s algorithm a link = a vote and the more votes a site has the more deserving it is of being ranked highly.
When a user is searching for something on a mobile phone two very important variables are added to the equation – time and location. These are so totally unrelated to links that it is impossible to use a link based algorithm to serve up relevant results. When you consider that very few mobile websites actually link out to other sites the issue becomes even more problematic.
Google has a patent that describes how a mobile algorithm could show results based on the users location, the time of day and their previous history. For example if you opened up Google at lunchtime it would display a list of phone numbers for your favourite local pubs before you even had to search for anything.
Opening up Google in the same location at midnight would bring up a list of local taxi firms and pizza shops, again without you having to search for anything.
Mobile algorithms are going to become more and more behavioural based as Google extracts more data from our mobile search habits. The key to ranking well in these algorithms is going to be very similar to the current online methods of ranking in Google Local.