How to downgrade iPhone 3G From 4.0 to 3.1?

[TurboJobo]

Hello I want to downgrade My Dad's iPhone 3G to some 3.X ios because he has 4.0 and omg its so slow and he dosent even use any of the IOS features he only uses the iphone as to make calls, some texts and play chess and a little of browsing so which one would you guys recommend me? 3.1.2 or 3.1.3 by the way i need the phone to be unlocked right know it is with 5.11.07 baseband
can you also leave me all the link to download everything i need and step through stem sorry if im asking for so much thanks in advance

 

[hackthatphone]

Here you go: http://www.hackthatphone.com/4x/downgrade_3g.html

No problem unlocking that phone with the modem version you have on it.