I have a line of pinpoint holes/calluses under my second toe on both feet. are they plantar warts, or something else?

SEE IT: Only by a doctor seeing it can a correct diagnosis be made.

Could be a virus: You may have verrucae, or plantar warts caused by the virus HPV though it is unusual to have a line of them. Other things that it could be is a parasite/worm, fungus or simple callus or corn. Less likely actinic keratosis. I would suggest your see a dermatologist to touch, diagnose, potentially biopsy and maybe shave or freeze it off if appropriate.