Carrier Settings update on iPhone, iPad

There are few cellular service providers who do not provide or release complete Carrier Settings. In that case you may have to enter APN settings manually on your device.

For example with Google FI, after the Carrier Settings Update on an iOS device one needs to manually enter APN Settings, which is h2g2. Only then the internet services will be enabled on an iPhone over cellular. Similar is the case for BSNL in India, the APN is bsnlnet

Based on your carrier (Cellular Service Provider) ask them for APN pin and enter it manually on your device. Alternatively you may search for the APN pin using any web search engine. After you have the APN pin with you then go to...

Settings > Mobile Data > APN Settings > [Mobile Data Section] Input APN which has been given to you by your Cellular Service provider.

If you do not have the above option that means the Cellular Service provider has released complete Carrier Settings Update. Read below

Carrier Update (Required): Released by your Cellular Service provider (Carrier Update), affects your Outgoing / Incoming calls, SMS, Data etc..

How to Update Carrier Settings

You can manually check for and install a carrier settings update with these steps: Make sure your device is connected to a Wi-Fi or cellular network. Tap Settings > General > About. If an update is available, you'll see an option to update your carrier settings.

Update your carrier settings on your iPhone or iPad - Apple Support