There are more than two. I do doubt that they have any support for voice effects with <strong> and <em>... if you run across a webpage that incorrectly uses these tags you may wonder why the page is always shouting at you.
I've personally tested with IBM Homepage reader.
As for CSS 2 /3 aural properties I haven't come across a single browser that imlpements any Aural CSS, likely to be a few years before we start to see that.
A PHP/C-Client/PEAR solution for webmail