One of the frustrating things is that Windows Mobile 5 no longer allows you to use the DisableCertChk utility to allow untrusted or invalid SSL certificates to be used. This is especially frustrating when you are just using the devices in a test environment. Here is a link on how to do a work around for the WM5 devices. http://geekswithblogs.net/wallabyfan/archive/2006/04/19/75608.aspx

Also, if you have a WM5 + MSFP (AKU2) device you can use the inexpensive GoDaddy Certificates instead of the pricey Verisign branded ones. For a complete list of compatible certificates check this out:

https://partner.microsoft.com/global/partner/40027352

 To talk about this in the forums:

http://www.exchangeexchange.com/forums/331/ShowPost.aspx#331