someone had a lot of time on their hands

Gotta try this it's cool....Here is a math puzzler so unbelievable that it will stump you. I would like to know who came up with this! Give it a try.

1. Grab a calculator. (you won't be able to do this one in your head)
2. Key in the first three digits of your phone number (NOT the area code)
3. Multiply by 80
4. Add 1
5. Multiply by 250
6. Add the last 4 digits of your phone number
7. Add the last 4 digits of your phone number again
8. Subtract 250
9. Divide number by 2

Do you recognize the answer?