On Android 4.1.2 that is on Samsung Galaxy S3, finding your phone number can be a little difficult. There is no “About Phone” option in setting.
1. Soft Left click, go to setting (bottom option).
2. Go to the very last option in the long menu, that is “About Device”
3. Click on second icon from top, that is “Status”
Your phone number is right in the middle of the list that says, “My Phone Number”.