APN (or "access point name") is a setting on your mobile phone that lets you access mobile internet.
Typically your APN is auto-configured or auto-detected for your phone or tablet and you don't need to make any changes to the APN on your device to get data service on your device. Wireless carriers have different pricing for different APNs; switching from one to another can change you from one type of data plan to another but make a mistake and it can also cause problems and additional charges on your wireless bill so fiddling with the APN isn't advised. However there are a few reasons people switch their APNs or modify them:
• The APN settings are not correct (you get error messages like "Could not activate cellular data network. You are not subscribed to a cellular data service").
• You have an unlocked phone and want to use it with a different carrier.
• You're on a prepaid plan and don't want to spend your minutes on mobile data.
• You're traveling outside of your wireless provider's service area and want to avoid data roaming charges.

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