Does the mailto work when you just hit the page from a standard web browser??
If so, you just might have a limitation of the Blackberry browser. There are ways around this: You could just submit the form to a standard server-side script (ASP.NET, ASP, PHP, JSP, whatever) that would then "forward" the email on to your desired target.
But if your mailto form doesn't even work with MSIE and FireFox on Windows, then show the <FORM> code here.