Quote from RCG's Girl:
Not funny, but cool. Where my math ppl?
Assume that phone number is "xyz"-"abcd"
Then, the steps become:
2) First 3 digits: xyz
3) Multiply by 80: xyz times 80
4) Add 1: xyz times 80 + 1
5) Multiply by 250: xyz times 20,000 + 250
6) Add the last 4 digits: xyz times 20,000 + 250 + abcd
7) Add the last 4 again: xyz times 20,000 + 250 + abcd times 2
8) Subtract 250: xyz times 20,000 + abcd times 2
9) Divide by 2: xyz times 10,000 + abcd
which equals => x,yz0,000 + abcd
which equals => x,yza,bcd (i.e. your phone number)
Will work for any 7 digit number. Any number of other math sequences could be done to provide the same result.