I see that there are some Motorola QIP2500-3 boxes on Ebay that are the exact same as the boxes I've got for Verizon fios. Does Verizon have to somehow activate these boxes or can I just buy one off ebay and start using it in my home?

Probably stolen.

Yeah, Verizon would need to activate it, and they're almost certainly not going to activate any random box that isn't in their inventory.

As bfoster said, it's generally assumed that eBay cable/sat/FIOS type boxes are either stolen or from a market outside the US. Either way, it'll be a brick.

Ok, thanks guys. Just trying to avoid paying the monthly fee for my boxes.

Heh, the eternal dream.