The simplest way to display a subVI's front panel is to modify the subVI's VI properties to show front panel when called and close front panel when finished. Look at the shipping examples called Dialog Box Demo and Popup Panel Demo. There are other options such as using VI server to programatically change a VI's properties, make more than one subVI visible at a time, continue exectution of the main VI while a subVI exectures. Look at the example called Ghost in the Machine and do a search for dynamically called VIs to find many more examples.
