Craigslist phone verification bypass cracked

Recently, craigslist has set up a phone verification to post ads on specific categories. We are looking to have a program developed to automate this process. The way it works now is. You must register an email address to post. It then asks for a phone number to call you, it gives a pin number and you must enter it into cl to activate your account to post. Your job is to figure out the algorythm craigslist is using and write a program that can take the inpur of the phone number and output the required craigslist pin.