For example just research the HAK5 PINEAPPLE. Lots of fun things you can do with that including watching what folk do, scrapping passwords and more.
But you suspected it, I can only confirm it.
As to device damage, since we can use social engineering to get folk to do the oddest things, then yes, the problem can extend to actual damage.
Maybe a silly question, but is it safe to use a second hand mifi device with a new SIM. By that I mean is it possible for there to be some malicious software within the mifi device that could steal data or damage devices linked to it?