The only thing you need is a recent version of Chrome (11 or up) and a microphone. And then...just by entering "x-webkit-speech" to the HTML Form Element Attributes of your input item, you have speech-enabled your application!
All "speech enabled" items will get a little mic at the end. When you click on it, you can say what you like. Oh yeah..and it works for number and date fields as well!
One remark : Whatever you enter will go through Google's voice recognition ... so Big Brother is listening in on you!
Try it out yourself on : http://apex.oracle.com/pls/apex/f?p=HTML5:SPEAK