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I have read that mobile phones will only support the accesskeys 0-9,*,# (for obvious reasons I guess).
On a more general note... Despite the trend not to use accesskeys these days for fear of making the site less accessible by clashing with browser/plugin defaults, I do favour a basic set of accesskeys myself. Since if the accesskeys do work then it does help IMHO. However, I would also give the user the ability to disable accesskeys across the whole site, either with JavaScript or (better) server-side. Another possibility is to allow the user to redefine the accesskeys themselves.
Perhaps the Accessibility and Usability [webmasterworld.com] forum might be able to offer further insight.