On an iPhone, use the Messages app.
pick the pencil icon in the top-right corner to start a new text message.
Add people in theTo: field.

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If they’re in your contacts list already, bang out their name and their contact info should appear.
Once you’re finished adding people, simply bang out your message, then tapSend.
Open your text message app.

On most phones, this will beMessages.
Open a new conversation.
Once you’ve picked your contacts, enter a message as usual and then selectSend.

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The setting will typically be a simple toggle switch in yourSettingsmenu, often under aMessengerorDatasubheading.
If those options are allowed, you should have no issue sending a group text.
That’s why knowinghow to leave a group message threadis always a handy skill to have.