3G is a wireless Internet connection provided by a cellphone company such as Verizon wireless. It allows a 3G device to connect to the Internet anywhere that a cellphone could have service. These devices require a contract from a cellphone provider and a monthly fee to use their service. Wifi connects to a local wireless network, such as those found in your home or at a coffee shop, to connect to the Internet. This is usually free but restricts you to only certain locations.