The best way to find this out is to give the router's serial number to a support representative or to a Fios equipment return-capable corporate store or authorized retailer. If your router shows as owned, no need to return. If your router shows as rent, then you need to return it to avoid being charged a replacement fee. If your router cannot be found on the system, then you cannot return it.
[Update] The Actiontec Rev. I has reached its end of support in Sep, 2020. Customers are advised to recycle the router themselves.