How to get someone to give me a mobile phone number.?

There is a company director who I need to get his mobile phone number without him knowing. How can I get it? I know his work number and his home number. I can also follow him so I know when he is not at home or at work. Any ideas?How to get someone to give me a mobile phone number.?Next time you are around his phone, just punch in yr cell phone number, and let it ring 1/2 times. You can go back to your phone and see from whom did you get a missed call!!