I don't anticipate Windows Mobile 6.5 being any problem as we run our application in the .NET Framework which is hosted by the device. As long as it's running Windows Mobile 2003 or later (which it is) and you can interact with the screen using a stylus, it should work. Feel free to download an evaluation from our web site and ensure compatibility prior to purchase. APDL Palm OS and Windows Mobile platforms are licensed separately. You can purchase a Windows Mobile license here.