This policy setting allows you to specify the fully qualified name or IP address for the proxy server used for Internet access ...

"This policy setting allows you to specify the fully qualified name or IP address for the proxy server used for Internet access by a Windows Mobile powered device when the Mobile VPN is active. The maximum length is 255 characters when you specify the fully qualified name.  A company can choose to have all Internet access pass through a proxy server to filter, audit, or restrict access.  If you do not specify a proxy server, the Windows Mobile powered device will forward all Internet traffic to the Mobile VPN gateway for appropriate routing. By default, no proxy server is specified.  Note: Only ASCII characters are supported for the fully qualified name of the server."