Chameleon, I read your idea and have decided that it is extremely flawed. First we'll start out with your program of choice, Brutus...
Since Brutus does not do random number/alphanumeric generation on the fly, it is impossible to do this without creating a list of numbers, which is the choice that you've made.
Now, 15 Digit numbers are extremely big. Especially in computer representation, lets just take as fact that each character in a text file is a single byte. If you want every number possible for the 15 digit numbers that is 999,999,999,999,999 unique numbers. Each one of those numbers containing 15 bytes of data. Sparing the board the math this comes out to be 14,305,114,746 MB
So unless you happen to be the CEO of google or IBM this method is a little over the top. We could remove the obvious numbers and still the amount of data this would require is enormous unless you reduce the amount of numbers to something thinkable like 9,000 at this point the numbers couldn't be sequential but would have to be random. This is what is most likely.. however a field of 9,000 is almost nothing compared to the amount of numbers tracfone can use and I don't personally know the usage of tracfone numbers but certainly there can't be more than 21 million active... so your chances of getting actives on your first try are little.
Now we consider your method of transmission.. brute forcing a web verification system. The problem with this is that you are going to be giving 9,000 HTTP requests from the same IP address... which im pretty sure tracfone may misconstrue as a Denial of Service attack although a poorly constructed one. So unless your planning on doing this through proxies that dont mind the FBI knocking this method isn't really recommended.
My suggestion: find another way to do it or give it up.