Iphone 3G how to downgrade baseband?

I have a iphone 3G on BB 61500(iPad bb) firmware 4.2.1 the last 3G firmware I believe I want to downgrade bb and unlock to all networks and be able to restore in iTunes to a new iphone so I can sell it. Question is is this possible and what BB should I use so iTunes don't put me in recovery loop thank for your replies

Here just visit this site download red-snow and click restore official base-band blog.iphone-dev.org/ that's it

There's no way that you can downgrade it. However you can take help from various internet sites or video tutorial. But its very risky I suggest don't try it.

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