I used geohot's BlackRa1n to jailbreak and unlock my friends phone.
It is a new iPhone 3GS (with updated bootrom). This of course means that once jailbroken the phone should not be turned off, otherwise it needs BlackRa1n to boot. After i unlocked, SIMs from other operators worked fine, wifi, etc. everyting was fine.

BUT, my friend did not like the idea of booting the phone from PC every time it goes off, so he asked me to restore it to the previous settings (iPhone locked only to one carrier).

I tried to make restore from itunes, (itunes automaticly downloaded the latest firmware and installed it), BUT when it booted, I was only able to do emergency calls, just like locker iPhone.

finaly:
Is it possible to restore the phone to the old settings?! Is it possible the phone to be locked to only one operator but to be able to boot normaly without using BlackRa1n.

Put the iPhone in dfu mode and restore using iTunes.

Set up iPhone as new.

It will be locked to the original carrier that your friend purchased it from.

Once the phone has been restored it will be locked to the original carrier again. You will need to use a SIM from the carrier it is locked to to activate in iTunes.