I found this, turns out Scarab already posted the site, but it has useful information.

http://www.hackcanada.com/blackcrawl/cell/assorted/trapfone.txt

In order to get free minutes, you have to hack the phones Nam memory bank, because if you try entering a second account on the phone, you’ll get the fallowing message “Location NAM error" . It’s not difficult and there is plenty of documentation on how to hack the phone’s NAM memory bank, here a couple sites that focus on hacking a Tracfones NAM memory bank:

http://www.hackcanada.com/ice3/cellular/index.html
http://www.nettwerked.net/TFA/cell.html

Once the Phone has been successfully hacked, you have to go into the NAM memory bank, which looks like the fallowing:

(1st) phone # - 555-555-5555
(1st) SID - 0 (A-side)

(2nd) phone # - [blank]
(2nd) SID - 1 (B-side)

In order to get free minutes, all you have to do is copy your phone information that is stored in the first block into the second block, once your number and SID have been copied into the second block, simply use your phone.
Like magic your phone works! However this is because Tracfone doesn’t have its own cell networks, so in order to prevent people from using more minutes then they’ve paid for, each Tracfone has a built in timer that will prevent you from using any more minutes than what you have paid for, however this is the only safeguard, once this is bypassed this by copying your phone number and SID number into the phones second block in the memory bank, you can talk to your hearts content! And who gets stuck with the bill you ask! Why, those bastard’s at Tracfone do! HA!
This works because Tracfone is pretty slow when it comes to updating account information to cell networks, so your phone will work fine until your accounts status has been updated on the cell network your Trakphone is using.
And thats how you rip off Tracfone. Have Fun!
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C++ Should Have Been Called "D"