Nice! These are probably the earliest of the digital StarTAC prototypes you've posted, judging from the keypads, which use the same font for the numerals/labels as the analog models. Motorola's original webpages for the ST7760 (here) and ST7790 (here) each show a photo of a phone with the same keypad as these, probably prototype units as well. The production units I've seen have keypads identical or similar to the other prototypes you posted. The lack of "Motorola" and "Digital" labels on the display screens further suggest these are early prototypes.