Neat Phone Number Math Trick

Just saw this, worked out for me. I'm sure there's a bunch of math stuff behind it, but let's just be kids again and enjoy the trick.

1. Key in the first three digits of your phone number (NOT the Area code…)
2. Multiply by 80
3. Add 1
4. Multiply by 250
5. Add to this the last 4 digits of your phone number
6. Add to this the last 4 digits of your phone number again.
7. Subtract 250
8. Divide number by 2

Do you recognize the answer ??
O.M.G. like magic!!!

Source: http://mymomisafob.com/2008/12/02/always-giving-us-more-math/