no internet, no router, no wifi
Nona: They can be used but you can not use Wi-Fi needed products such as apps, or go on Google and search a question (Which means no accessing websites etc). Pretty much know you know this far, however their is games (Apps in Google Play-Store), (But you can't download them without Wi-Fi), which you can play without Internet connection.
They can be used by connecting to a cellular 3G/4G network, but it may cost more than a wired internet connection. The advantage is that you can use the internet anywhere that has a phone signal.
Sure you can, but you won't be able to get online, social , or download/buy apps. having devices without internet is useless. no fun.
Yes, via the cell tower.