Ipad wifi cellular

If you have added a DataSIM and Cellular plan to a WiFi+Cellular model of iPad, the number associated with the SIM card is only used to identify your account for billing purposes. This number is not used for making calls or sending messages.

If previously provisioned, you can find the “number” associated with your iPad from Settings:

Settings > General > About > Mobile Data Number

If “unknown” is shown, a cellular plan has not been provisioned, the active SIM has been removed, or the Cellular SIM/plan has been cancelled.

iPads wifi+cellular models do not have "phone" capability. They use SIM cards just for cellular data (when wifi network is not available/reachable).

You can ask your cellular carrier about the number tied to your data SIM card, but that number doesn't mean anything for "phone" purposes.

Regards

Giulio