Good question!
I'm about to start developing the paysite's mobile tours and was thinking about that ...
I would use the cell-phones higher screen resolution if you are talking for showing whole picture to surfer, like clicking on a link to see the picture itself.
They would still be of a very small size on disk so you may have some different size pictures for different screen resolutions and you could easily fix image paths according to user agents ( Screen Resolution ) ;P
I will do that ;) If you need help, let me know
