NO, it is not "illegal to drive and use a mobile device" -- different areas have different laws (or none at all) about using mobile devices, but I have yet to see or hear of anywhere that completely bans all mobile use of all mobile devices.
Throughout the United States (where your Tennessee is located, for example) many states and cities ban cell phone use UNLESS you are using a 'hands free' device (such as a speakerphone or headset). Some of these laws are written very broadly in an effort to make sure they cover texting and gaming on cellphones etc, but all include numerous exemptions.
Also, all the legal bans apply only to the driver -- so there are no bans when riding with someone else driving, including riding in a taxi, train, bus, etc.
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