Wifi has nothing to do with the iPhone Family. Wifi is wireless connecting of networking devices (Playstation, PC, iPhone, etc.) instead of WIRES plugged into your devices to get on the network (network is interconnected devices wired or wireless that see each other). The Netgear WITH a service provider (AT&T) connects your home (for a monthly fee) to AT&T then to the rest of the world (Internet).
Your iPhone, like all smart phones, has TWO capabilities. First is Cellular (those 'cell towers' people see) that is used by phones for voice, then additionally Internet access. Cell towers have to be 'in range' (those 'bars' you look at on the phone) to get the signal for voice or Internet access. But using the Cellular service for Internet used to eat up 'minutes' and now has a 'usage cap' on how much you can do in a month, so they added Wifi to the phones.
Just like a laptop the wifi picks up on the smart phone to use for Internet, but doesn't 'cost' you on your phone bill. Wifi though, is not like cellular that it is everywhere, it is ONLY in range of a single building, and they have to be letting you use it (McDonalds, a Hotel, Starbucks, your library, your home). If you aren't authorized then you can't use the Wifi even if your iPhone/cell phone picks it up, or even if it was your laptop that picked it up.