Nokia have a toolkit (windows only, despite the fact it's written in Java) which includes a simulated WAP 1.1 phone (Nokia 7110) as well as a prototype WAP 2.0 (XHTML) phone.

I believe that phone.com also have some emulators available for download (based on their browser which phone manufacturers have licensed).

The major problem I have with developing for WAP is getting the size of the page down in all cases.

For the Nokia 7110 (which I have) the compiled size of the page must be less than 1400 bytes or so or the page just won't load - this is a real pain since all our pages are dynamic and it's difficult to ensure that the page won't spill - every page on the site has to automagically have 'next page' links added to it.

Still, on the upside - the pages I have done do look good and are a pretty useful cut down version of our site, which converts to a 'mobile' form pretty well.

Have fun,

rdw