pocket pc's running microsoft pocket pc os can somehow offer you a sort of security, you can use VPN for your pocket PC's connection to your network, VPN connection gives you an audit trail on who and when a particular pocket PC logged in to your network, that gives ya clues in tracing.

as for e-mail security the Pocket PC implements the ability to authenticate the user before allowing the user to send e-mail. The authentication method supported is called Secure Password Authentication (SPA) which MSN and Exchange support. This feature allows remote users to send e-mail through a server without opening that e-mail server up to spammer abuse.

So if you are requiring more advanced security in your network, the Pocket PC access will vary from no access to limited access to network resources.