Many Android tablets are sold as Wi-Fi only devices. On these devices, you use whatever Wi-Fi network you use for your laptops; and when you’re out of Wi-Fi range, you can’t connect to the Internet. Even tablets that are sold with 3G or 4G data access can be used with Wi-Fi networks. In fact, if you don’t purchase separate data access from a cell phone service provider, that’s your only option.
Some tablets, such as the T-Mobile G-Slate, allow you to buy short-term, pre-paid data plans just as you would on a 3G iPad. Others, such as the Motorola Xoom (at the time of writing), either don’t offer pre-paid monthly service or make it prohibitively expensive. So far, all the tablets with 3G/4G data plans have a contract option that gives you a discount on the purchase price of the device, while also locking you into a monthly data contract for two years—mirroring the model used for most cell phones.
NOTE: If your tablet didn’t come with at least 3G access, you can’t add it later. The Motorola Xoom shipped with 3G-only access, but users can upgrade the connection to 4G. However, most tablets cannot be upgraded in this way.