Here is another math trick This will work only with 7 digit Phone No. 1. Grab a coluclatar. (You wont be able to do this in your head)2. Key in the first three digits of your phone number (NOT the area code)3. Mutiply by 804. Add 15. Mutiply by 2506. Add the last four numbers of your phone number7. Add the last four numbers of your phone number again8. Subtract 2509. Divide number by 2 Do you recognize the answer? IS'NT IT YOUR PHONE NO:?