How to unlocked 3g after downgrade to iOS 3.1.3

[dudu]

My legally purchased US, 3g iPhone, become locked after iOS downgrade to 3.1.3. I receive an iTunes message that "There is no SIM card installed in the iPhone you are attempting to activate" and when I put my SIM the message changed to "the SIM card inserted in this iPhone does not appear to be supported? and ? Only compatible SIM cards from a supported Carrier may be used to activate iPhone?" ? I do not have any other SIM and I'm outside the US.
By using Redsn0w 9.6 I receive a note "Unable to recognize specified IPSW" (regarding the ver. iPhone1,2_3.1.3_7E18_Restore I installed)...

please HELP

 

[Ipheuria]

Your phone hasn't become locked it just needs to be hacktivated. You need to reload the firmware with a custom one made with Pwnage Tool using the hacktivate option. Then once you get into your phone you'll be able to see what baseband it's running. Either send me a PM or look on my bio and email me I'll make you the ipsw. It will wipe your phone so make sure hopefully you have a backup of your phone. You said iPhone 3G with firmware 3.1.3 right?