Where to find samsung galaxy tab s phone number

Solution
Maybe there is no SIM card in your phone. Did it come with a contract or are you free to buy a SIM of your own and pay in advance for calls and data?
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There has to be a SIM card - a small piece of cardboard with some printed circuits and a little triangle missing from one corner.

You can buy one that allows you to add some credit to it and use that up making calls before topping up the balance again. Alternatively, you can enter into a contract with a company who will provide you with a SIM card and pay monthly in advance with the call and data costs accruing and payable.