My iPhone Is Telling Me That I Am Not Subscribed to a Cellular Data Service
Turn cellular data to on in your settings. Additionally read your manual located on your phone or read it at http://www.apple.com from a tablet or regular computer.
Let's ensure that you're able to use your device to its fullest abilities. As @electorny mentioned it is important that your data is on. This feature may be adjusted by heading into Settings > General > Cellular > Cellular Data - On. In addition, it is always beneficial to complete a soft by holding the power button and the home button simultaneously until the Apple symbol appears. This may take about 10 seconds. This is similar to powering down a computer.
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