Really the answer is no in most cases. Many browsers support tags that will in some way change the font making it bold, italic etc, but the typeface itself can probably not be changed. I have yet to see a browser that can, and there is no tag in WML specifically for this.

For those of you who have access to the PHP script language or another script language that has GD support, WBMPs with TrueType fonts and even Postscript fonts can actually be generated on-the-fly.