In order to allow WAP/WML on IIS 5.0, 6.0, you just need to add a few MIME types. Follow the below steps.

[1] Start Menu => Control Panel => Administrative Tools => Internet Services Manager
[2] Right Click on the computer/server/machine name and select Properties
[3] Click Computer MIME Map => Edit existing MIME types=> Click New Type and add the below mentioned MIME types
a] .wml, type text/vnd.wap.wml
b] .wmlc, type application/vnd.wap.wmlc
c] .wmls, type text/vnd.wap.wmlscript
d] .wmlsc, type application/vnd.wap.wmlscriptc
e] .wbmp, type image/vnd.wap.wbmp