I have two iphones one is 3g and the other is 3gs,both version 3.13. I would like to unlock and jailbreak both myself online without incuring any costs. I have the necessary cable. please advise/assist. thanks

You said their both 3.1.3, that means, unfortunately, there is no available unlock for this version. But luckily, its both jailbreakable!
No need to pay anything, just go here: http://spiritjb.com/
download the appropriate Spirit for your computer (either Windows, Mac, or Linux).
Once you complete the download, plug your one iPhone to your computer and run the Spirit application.
The Spirit window will pop up. It has a single button saying "Jailbreak". Click that button and wait for about 20-30 seconds. After that, it's all done!
Again, there is no unlock available yet.
For more iPhone / iPod touch tips, click here.
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