Citrix is porting XenApp to the iPhone. XenApp is a remote Windows application that is presently available for Mac, Windows and some mobile platforms. XenApp allows users to remotely log into their corporate networks to access their Windows applications.

The functionality seems similar to existing VNC clients for the iPhone, but Citrix's XenApp apparently transmits window display information rather than the raw graphics (wikipedia link ^[1]). This is much better than VNC over network connections such as 3G and WiFi.