Programmatically obtain the phone number of the Android phone

Question

How can I programmatically get the phone number of the device that is running my android app?

Answer 1

Just want to add a bit here to above explanations in the above answers. Which will save time for others as well.

In my case this method didn't returned any mobile number, an empty string was returned. It was due to the case that I had ported my number on the new sim. So if I go into the Settings>About Phone>Status>My Phone Number it shows me "Unknown".