I bet you won't find any Windows Mobile user today who seriously uses his phone to browse the web using Internet Explorer Mobile.
Opera Mobile runs on all Windows Mobile devices that I've had over the past 10 years, and the last 6 years or so it came pre-installed with every phone that I had. It's a pretty decent browser. Most popular JavaScript frameworks even work, as long as they don't use too much html5, css3 or SVG trickery.
Internet Explorer Mobile should be entirely ignored, especially if you plan on doing client-side scripting. www.microsoft.com and live.com don't even load with that crappy browser.
If somehow you're forced to develop a dynamic website for IE mobile, you're pretty much screwed. I've done it in the past. Please don't make the memories come back. It left permanent scratches on my soul.