Adding speech input to your webapp is much easier than it might first seem.
This is part of the proposed HTML5 enhancements to FORMS and is already implmented in some browsers.
Google Chrome (WebKit 534.24) added this in version 11 in April 2011.
XHTML compatible example:
<input type="text" x-webkit-speech="x-webkit-speech" speech="speech" value="" />
In this example, ‘x-webkit-speech’ is the proprietary attribute used by Google Chrome (WebKit). ‘speech’ is the expected HTML5 attribute when it is finalized.