I have been following the posts regarding Icons and I still couldn't get them to display on my 3790T until today.
I opened the bitmap in Photoshop and checked it was 8 bit and 22 x 22 as per other posts. The image would not display until I changed it from RGB to Indexed. It defaulted to 6 colours so I went with that and it finally showed up.
The icon was quite small however it was readable.