How to check your MTN number on your mobile phone is done by dialing series of codes and following the commands appropriately.
There are various ways to check for your MTN number on your smartphone, I would be giving you the two easiest ways to go about it.
How to Check your MTN number using USSD Code
You can check your MTN Number by dialing *663# and you get a message containing your mobile number.
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you can also visit the MTN self-service center by dialing *121# to stay connected.