sony ericsson K750i as remote control for keynote?

you can use Salling Clicker to do an excellent job of that but i think it costs about $30. It does plenty of other things as well but if you're wanting a free solution then you should download Sony Ericsson's bluetooth remote control editor and then you can make a remote profile which will interpret your key-presses on the phone as keys on the keyboard or combinations of keys on the keyboard. You can then send this to your phone and then access it through the entertainment pane. Salling clicker offers a much more refined solution where you can go from on the desktop to the end of your presentation without even touching the mac. The other solution would require you to open up your presentation and would only allow simple navigation through the presentation.

i hope this helps