Its Your Phone No

ITS YOUR PHONE NO
I thought this was kind of interesting... Someone send this to me, and I was about to delete, then i thought why not give it a try, like I knew its a trick but still I wonder how they came up with that
1) Key in the first three digits of your phone number into a calculator. (do not use your area code number)
2) Multiply by 80
3) Add one
4) Multiply by 250
5) Plus last four digits of your phone number
6) Plus last four digits of your phone number again
7) Minus 250
8) Divide by 2
Is it your phone number?
hay naa???????????