Need 3g downgrade instruction

[HappyTroller]

Hi guys,
i have a mate with a 3G, 4.2.1, and he wants to downgrade to 3.1.3 without loosing contacts and still be able to get music on it. unlock is not needed. i just need a tutorial.
Please help.
thank you.

[i.Annie]

If the music is in the iTunes library still, it can always be synced back in after the downgrade. Contacts: go to info tab, click to sync with Windows Contacts, then they will be able to be synced back in the phone after downgrading.

To downgrade, download stock 3.1.3 ipsw. You can get it in the Downloads section here on MMi. Go to iTunes, hold shift and click restore. Select the 3.1.3 ipsw. Then the restore should finish and it should be fine.

If you receive error 1015, simply exit recovery mode with TinyUmbrella.