The SBS/Skyline Algorithm
by Nynex Phreak

SBS Skyline has one of the easiest methods of finding codes of all of the long
distance companies. It's very similar to the old Sprint bug which allowed
people to find codes very quickly, even without the use of a computer.
To see how this method works, access SBS Skyline at their equal access number
(950-1088). Enter six digits. These are the six digits you are "betting" on
to be part of a valid code. After the six digits, enter five other numbers
(it's not important what numbers they are). If you hear a ring immediately
after the last number, followed by "Message MS2", the six digits are part of
a valid code. If you don't hear a ring, hit the pound sign (#) key. If you
get your tone back, the six digits were not part of a valid code. You can try
a new six digit series without having to hang up and redial. This is what
makes this method so fantastically easy. (If you don't get your tone back
after hitting the pound sign and also don't get "Message MS2", chances are
you've stumbled across one of those SBS toll-free numbers. This might also be
the case if you get "Message MS2" before entering five additional numbers.)
After finding a working set of six digits, all that must be done is to
find the next one or two numbers of the code. Enter the six digit code,
followed by an additional one number to guess, followed by four random
digits. If it rings and gives "Message MS2", this is not the right guess.
You must hang up and redial Skyline for each unsuccessful attempt at this
point. If it doesn't ring, and you can get the tone back by hitting the pound
sign, you have found a seven digit code. If you try all the numbers from zero
to nine and they all give "Message MS2", then you have two digits to
guess--your six digits are actually part of an eight digit code. The same
method must be used, except your range is now from 00 to 99.

2600 Magazine, Volume 3, Number 5, May 1986