WAP/WML Mobile Phone Compatibility Issues

I've been developing WML pages for almost a year now and recently I
found that some of my pages, while they validate perfectly at
http://www.validome.org/validate against their respective WML DTDs, do
not show up in all browsers. Specifically, Blackberry, Motorola and
some Samsung phone browsers are causing the most problems. Both are
very new and shouldn't have a problem reading a WML 1.1 xml doc. Is
there anyone out there that has had a similar experience?

FYI, I'm developing in a LAMP architecture for all of the WML, but most
files are just pure text/wml that results in Internal Errror or some
variation of Page Cannot be Displayed.