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I'm sorry, the iPad doesn't support phone calls (via carrier network) like your mobile phone. If you have the iPad with SIM supported model, then that is only for accessing internet. This is how Apple designed it.
However, there are some solutions to make phone calls from iPad using internet or WiFi. You can setup Facetime (from Settings > Facetime) to make calls to other Apple users.
You can use Skype or Google Voice to make phone calls from iPad. Open App Store, search Skype and/or Google Voice. Install them and use them to make calls from iPad.
If you have any questions or would like any additional information, please don't hesitate to ask.
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