3.1H is the highest you can go for Operating System on a Visor Deluxe. If you have an older Deluxe you would be able to upgrade to that 3.1H.
I bought a Deluxe in December and it shipped with 3.1H installed. That was about the only thing I didn't like about the Deluxes. That you can't upgrade the OS. When looking for programs to download, there are a number that don't support the old OS. But it's not like there's nothing out there because there is a lot.