This site is about the HP-Compaq iPAQ H3900, which was a Pocket PC 2002 device released by HP in 2002. You can find more information on Wikipedia.
H3900 picture (from HP's website)
How can you tell if your device is a H3900? Well, if it looks like the device above it's probably a H3900. Check on the back and find the serial number, as that will definitely tell you.