Instead, just use the tethering or Wi-Fi hotspot feature on your smartphone. If your current cellular plan doesn't include any tethering or hotspot data, you may have to pay extra to get it--but that'll likely be cheaper than a separate cellular contract, and you'll be able to get any of your devices online from anywhere.
Just enable the Wi-Fi hotspot feature on your smartphone's settings screen and connect your Chromebook to it like you'd connect to any other Wi-Fi network. To avoid your phone's battery dying, you can plug it in via a USB cable and it'll draw power from your Chromebook. Chromebooks also support USB tethering, so when you plug your phone into the Chromebook with tethering enabled, it should connect to the Internet through your Chromebook via the USB connection. This USB tethering should work well with Android phones. Chromebooks can't tether via Bluetooth, however.
This is probably the best option for most people. Just let your phone be your Chromebook's lifeline to the Internet and worry about the single device's data plan.
Control your data usage
Google's new Data Saver extension for Chrome will help you reduce data usage when tethering via your Chromebook. Enabling click-to-play plugins will also help, preventing your Chromebook from automatically downloading and playing Flash advertisements and videos on the web.
Chrome includes settings for many different things--heck, you could even disable all images on the Internet in Chrome's settings screen to save on data. But the most important thing is realizing your data is being metered and planning accordingly. That means avoiding videos, music, and big downloads. If you really only have 200MB of free data a month, be sure to make it count and only use it in a pinch.
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